Tax Q&A in category: Investments, Property & Inheritance

Question 1

What Is a QEF Election and How Does It Reduce My PFIC Tax?

Accepted Answer

A Qualified Electing Fund (QEF) election under IRC Section 1295 lets you include your share of a PFIC‘s ordinary earnings and net capital gains on your U.S. return each year, even if no distribution is made. This avoids the default Section 1291 regime, which imposes the highest ordinary income tax rate plus compounding interest on excess distributions and sale gains.

How the QEF election works:

Annual inclusion: You report your pro-rata share of the fund’s ordinary income and net capital gains each year on Form 8621
Capital gains rate preserved: The net capital gain portion qualifies for preferential long-term capital gains rates (0%, 15%, or 20%)
No interest charge: Because income is recognized annually, the punitive Section 1291 interest charge does not apply
Basis increases: Your basis in the PFIC increases by the amounts you include each year

FeatureSection 1291 (default)QEF electionTax rate on gainsTop ordinary rate + interestOrdinary + capital gains ratesWhen income recognizedAt distribution or saleAnnuallyInterest chargeYes, compoundingNoCapital gains rate availableNoYes Requirements to make a valid QEF election:

PFIC Annual Information Statement (AIS): The fund must provide this document, or you must obtain equivalent data from the fund’s financial statements
Timing: Ideally elected in the first year you hold the PFIC. If elected after year one, a “purging election” under Section 1291(d)(2) may be needed to clear prior-year Section 1291 taint
Filed with Form 8621: Attach to your timely filed return (including extensions)

If you hold foreign mutual funds or ETFs classified as PFICs, the QEF election is typically the most favorable tax treatment available, provided the fund supplies the necessary data. For the PFIC election strategy, see our PFIC Reporting Guide.

Question 2

Do I owe U.S. taxes on my UK ISA or other foreign tax-exempt investment account?

Accepted Answer

Yes, the UK ISA (Individual Savings Account) and similar foreign tax-exempt investment accounts are fully taxable on your U.S. return. The U.K. exemption does not carry over to U.S. tax. If the ISA holds foreign mutual funds, most are PFICs, and you must file Form 8621 each year for each fund held.

Why foreign tax-exempt accounts are not U.S. tax-exempt:

U.S. tax code recognizes only specific U.S. shelters (IRA, 401(k), HSA, 529)
No treaty generally extends foreign tax shelter status to the U.S.
Dividends, interest, and gains inside an ISA are U.S. taxable

Common foreign “tax-free” accounts and U.S. treatment: AccountCountryU.S. treatmentISA (Cash, Stocks & Shares, Lifetime)UKFully taxable; PFIC riskTFSACanadaFully taxable; possible trust reportingPEAFranceFully taxable; PFIC risk on fund holdingsPlan Epargne PopulaireFranceFully taxableSingapore SRSSingaporeTaxable at distribution Reporting stack for a UK Stocks & Shares ISA:

Schedule B: Dividends and interest
Schedule D / Form 8949: Gains/losses on sales
Form 8621: Per PFIC per year (often one per fund)
FBAR: If aggregate over $10k
Form 8938: If threshold met

Planning notes:

Cash ISA is the simplest: just the interest is taxable
Stocks & Shares ISA with foreign funds: PFIC burden is often severe
Consider individual stocks or U.S. funds held in taxable accounts instead

For UK ISA and PFIC filing help, see our PFIC Reporting Guide.

Question 3

How Do U.S. Estate Tax Treaties Protect Non-Resident Property Owners?

Accepted Answer

Non-resident aliens (NRAs) who own U.S. property face federal estate tax at rates up to 40% on U.S.-situs assets above a $60,000 exemption, far below the $13.99 million exclusion for U.S. citizens. U.S. estate tax treaties with 16 countries can dramatically increase the effective exemption, prevent double taxation, and grant access to the marital deduction.

The NRA estate tax problem without a treaty: ItemNRA (no treaty)U.S. citizenExemption$60,000$13,990,000 (2025)U.S.-situs assets subject to taxReal estate, tangible property, U.S. stocksWorldwide assetsTop rate40%40%Marital deductionNot available (unless QDOT)Unlimited for a U.S. citizen spouse How treaties help:

Pro-rata unified credit: Many treaties (including the UK, Canada, Germany, and France) grant NRAs a share of the full U.S. unified credit proportional to their worldwide estate. If U.S. assets are 10% of a $5 million worldwide estate, the effective exemption rises well above $60,000
Situs rules modified: Some treaties exempt certain assets (bank deposits, debt obligations) from U.S. estate tax
Double tax relief: Credits for estate tax paid in either country on the same assets
Marital deduction access: Several treaties extend the unlimited marital deduction to non-citizen surviving spouses without requiring a QDOT

Countries with U.S. estate and/or gift tax treaties:

Australia, Austria, Canada, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Japan, Netherlands, Norway, South Africa, Switzerland, United Kingdom

Planning considerations for NRAs:

Review treaty provisions before purchasing U.S. real estate or stocks
Consider holding U.S. property through structures that may shift situs (with professional guidance)
File Form 706-NA to claim treaty benefits; the treaty election must be made on the return

For estate and inheritance planning, see our Estate Planning and Inheritance Taxes Abroad.

Question 4

Is Money from a Foreign Relative a Gift or a Loan for U.S. Tax Purposes?

Accepted Answer

The IRS classifies money received from a foreign relative as either a gift or a loan based on the transfer’s intent and terms. A gift triggers Form 3520 reporting if it exceeds $100,000 from a nonresident alien individual in a year. A loan creates no Form 3520 obligation but may trigger imputed interest rules if the terms are below-market.

How the IRS decides gift vs. loan: FactorPoints toward a giftPoints toward a loanWritten agreementNoneSigned a promissory note with termsRepayment scheduleNo expectation of repaymentFixed installments or maturity dateInterest rateNo interest chargedAt or above IRS AFRActual repaymentsNone madeDocumented payments over timeCollateral or securityNonePledged assets Why the classification matters:

Gift over $100,000: You must file Form 3520 (Part IV) with your return. The gift itself is not taxable, but the penalty for not filing is 5% per month up to 25% of the amount
Loan with below-market interest: The IRS imputes interest at the Applicable Federal Rate (AFR). The difference between the AFR and the rate charged is treated as a gift from the lender to you, and as interest income to the lender
Loan recharacterized as a gift: If the IRS determines there was never a real expectation of repayment, the entire amount becomes a reportable foreign gift

Protecting yourself:

Document every transfer with a written agreement in both languages
Use a market interest rate (at least the AFR for the loan term)
Make actual repayments and keep wire transfer records
Report on Form 3520 if there is any doubt; over-reporting is safer than under-reporting

For foreign gift reporting guidance, see our Form 3520 Guide.

Question 5

Do I Owe Tax on Currency Exchange Gains When I Sell Foreign Property?

Accepted Answer

Yes, when you sell foreign property, you may owe U.S. tax on two separate gains: the capital gain on the property itself and a Section 988 ordinary income gain from currency fluctuations on your foreign mortgage. Section 988 of the Internal Revenue Code treats gains and losses from changes in exchange rates on certain foreign currency transactions as ordinary income or loss, taxed at your regular income tax rate rather than the lower capital gains rate.

How Section 988 currency gain arises on a property sale:

You borrow in foreign currency (e.g., a GBP mortgage on a UK home)
Over time, the USD weakens against that currency (or the foreign currency strengthens)
When you repay the mortgage at sale, the USD cost of repaying exceeds the USD value when you originally borrowed
The difference is a Section 988 ordinary loss (favorable). If the USD strengthened instead, you would have a Section 988 ordinary gain

Example (UK property with GBP mortgage): ItemGBPUSD equivalentMortgage taken in 2018GBP 300,000$405,000 (rate 1.35)Mortgage repaid at sale 2025GBP 300,000$378,000 (rate 1.26)Section 988 ordinary gain$27,000 (USD cost decreased) Key points:

Section 988 gain is ordinary income, not capital gain, so it does not qualify for the lower long-term capital gains rates
The Section 121 primary residence exclusion does not shelter Section 988 gain on the mortgage
Foreign tax paid on the property sale may be creditable via Form 1116, but matching the credit to the Section 988 portion requires careful allocation
No Section 988 issue if you purchased in cash with no foreign currency debt

Reporting: Section 988 gains are reported as “other income” on Schedule 1 (Form 1040), Line 8z. The property capital gain goes on Form 8949 and Schedule D separately.

For foreign property sale tax help, see our Foreign Capital Gains Guide.

Question 6

Do I Get a Step-Up in Cost Basis for Inherited Foreign Property?

Accepted Answer

Yes, under IRC Section 1014, inherited foreign property receives a step-up in cost basis to fair market value (FMV) on the decedent’s date of death, converted to USD at that date’s exchange rate. This applies whether or not U.S. estate tax was owed, and regardless of the decedent’s citizenship or the property’s location. The step-up can dramatically reduce or eliminate your U.S. capital gains tax when you eventually sell.

How the step-up works for foreign property: ItemHow to determineDate of death FMVLocal appraisal, comparable sales, or foreign tax authority valuationUSD conversion rateTreasury rate or published rate on the date of deathAlternate valuation dateSix months after death (Form 706 election only, if estate tax return is filed)Improvements after inheritanceAdd to stepped-up basis at USD rate when paid Example (inherited French apartment): ItemEURUSDDecedent’s original purchase price (2005)EUR 200,000$240,000FMV on date of death (2024)EUR 450,000$495,000 @ 1.10Your stepped-up basis$495,000Sale price (2026)EUR 470,000$493,500 @ 1.05U.S. capital gain$0 (loss of $1,500)

Without the step-up, you would have owed tax on $253,500 of gain. With it, you have a small loss.

What does NOT get a step-up:

Property received as a gift during the donor’s lifetime (you take the donor’s basis, not FMV)
Property in a revocable grantor trust in some foreign jurisdictions, where the trust structure may not qualify under Section 1014 (seek professional advice)
Property the decedent received as a gift within one year of death, and that passes back to the original donor

Documentation you need:

Death certificate and will or succession documents
Independent appraisal or government tax valuation at the date of death
Exchange rate source (Treasury, OANDA, or bank record)

For inherited property tax planning, see our guide on Avoiding Capital Gains Tax on Inherited Property.

Question 7

What Is the Tax on Selling Inherited Property Overseas?

Accepted Answer

When you sell inherited property overseas, you owe U.S. capital gains tax on the difference between the sale proceeds (in USD) and your stepped-up cost basis. Inherited property automatically qualifies for long-term capital gains treatment regardless of how long you held it, and any foreign tax paid on the sale is creditable on Form 1116.

Step-by-step calculation: StepWhat to do1. Determine stepped-up basisFMV on date of death, converted to USD at that date’s rate2. Add improvements after inheritanceUSD cost of any capital improvements you made3. Calculate sale proceeds in USDSale price in foreign currency x exchange rate on closing date4. Subtract selling costsAgent commissions, notary, legal, transfer taxes5. Compute gainProceeds minus costs minus stepped-up basis Example (inherited Indian property): ItemINRUSDStepped-up basis (date of death 2022)INR 30,000,000$375,000 @ 0.0125Sale price (2025)INR 35,000,000$416,500 @ 0.0119Selling costsINR 1,750,000($20,825)U.S. capital gain$20,675Indian capital gains tax paid$25,000Form 1116 credit($20,675 limited to U.S. tax on gain) Key tax rules:

Always long-term: Inherited property is treated as held for more than one year, qualifying for 0%, 15%, or 20% rates
Net Investment Income Tax: An additional 3.8% may apply above MAGI thresholds ($200,000 single, $250,000 MFJ)
Foreign tax credit: Claim foreign capital gains tax paid on Form 1116 (passive category). If foreign tax exceeds U.S. tax on the gain, the excess carries forward
Section 988 currency gain: If you repay a foreign mortgage at sale, any currency gain on the debt is ordinary income reported separately

Filing requirements: Report the sale on Form 8949 and Schedule D. File Form 3520 in the year you received the inheritance (if over $100,000).

For inherited property tax planning, see our guide on Avoiding Capital Gains Tax on Inherited Property.

Question 8

What Can I Include in the Cost Basis of My Foreign Property?

Accepted Answer

Your cost basis for foreign property includes the USD-equivalent purchase price on the closing date, plus all acquisition costs (stamp duty, notary fees, legal fees, registration taxes, agent commissions) and capital improvements made after purchase. Each component is converted to USD at the exchange rate on the date the expense was paid, and that USD amount is locked in permanently.

Items included in cost basis: ItemIncluded?NotesPurchase priceYesForeign currency amount x rate on closing dateStamp duty/transfer taxYesCommon in the UK, France, Spain, and AustraliaNotary and legal feesYesBoth the buyer-side and required seller-side fees you paidRegistration/land registry feesYesGovernment recording costsBoth the buyer-side and seller-side fees you paidYesNot all countries charge buyer-side commissionCapital improvementsYesRenovations, additions, structural upgrades (each at the rate when paid)Repairs and maintenanceNoDeductible as rental expense on Schedule E if rented, but do not increase basisFurniture and appliancesSeparateDepreciated as personal property, not part of the real property basis Currency conversion rules:

Each cost is fixed in USD on the date incurred, not the date you file
Do not re-convert at sale: Your basis stays at the original USD amounts
Section 988 currency gain on a foreign mortgage is computed separately from the property gain itself

Land vs. building allocation:

Only the building portion depreciates (30-year ADS for foreign residential rental placed in service after 2017)
Use the local tax assessment split, a professional appraisal, or the allocation in the purchase contract
If no local data exists, 20% to 30% for land is a common starting point for urban properties, but document your method

Reducing basis:

Depreciation taken (or allowed) on the rental portion
Casualty losses previously deducted
Insurance reimbursements for damage

For foreign property sale tax planning, see our Buying and Selling Real Estate Abroad.

Question 9

How Do I Get a Refund of FIRPTA Withholding After Selling U.S. Property?

Accepted Answer

To get a refund of FIRPTA withholding, file Form 1040-NR for the year you sold the property, report the actual capital gain, and claim the 15% withholding as a tax payment on line 25d. Because FIRPTA (Foreign Investment in Real Property Tax Act) requires the buyer to withhold 15% of the gross sale price via Form 8288, the amount withheld almost always exceeds your actual tax liability on the net gain. The IRS refunds the difference after processing your return.

The FIRPTA refund process step by step: StepActionForm1Buyer withholds 15% of gross price at closingForm 8288 / 8288-A2You receive Copy B of Form 8288-A showing the amount withheldRetain for your records3File a U.S. tax return for the sale yearForm 1040-NR4Report the sale on Schedule D / Form 8949Capital gain calculation5Claim the FIRPTA withholding as a tax paymentForm 1040-NR, line 25d6IRS processes the return and issues a refundDirect deposit or check Why you almost always get a refund:

15% is withheld on the gross sale price, not on the gain
Your actual tax is on the net gain (sale price minus basis minus selling costs), taxed at capital gains rates (typically 15% or 20% of the gain)
Example: Sell for $500,000 with a $400,000 basis. FIRPTA withheld: $75,000. Actual tax on $100,000 gain at 15%: $15,000. Refund: $60,000

Timeline and tips:

File Form 1040-NR as early as possible after year-end; refunds typically take 6 to 12 months
ITIN required: If you do not have a Social Security number, apply for an Individual Taxpayer Identification Number (Form W-7) and attach it to your 1040-NR
Withholding certificate (Form 8288-B): To reduce withholding at closing, you can apply before the sale, but processing takes 90+ days
State withholding: Many states (California, Hawaii, Maryland, others) impose separate state-level withholding on foreign sellers, also refundable via a state nonresident return

For help with FIRPTA and NRA filing, see our Form 8288 Guide.

Question 10

How Do Multiple Heirs Report a Shared Foreign Inheritance to the IRS?

Accepted Answer

Each U.S. person who receives more than $100,000 from a nonresident alien individual or foreign estate must file their own Form 3520. When siblings or other heirs share a foreign inheritance, every qualifying heir files separately based on their individual share, and each tracks their own cost basis if property is involved.

Form 3520 filing for multiple heirs: ScenarioWho files Form 3520?3 siblings inherit $450,000 total ($150,000 each)Each sibling files (each exceeds $100,000)3 siblings inherit $240,000 total ($80,000 each)No filing (no one exceeds $100,000)2 siblings: one gets $200,000, the other gets $50,000Only the $200,000 recipient filesInheritance received in installments over the yearsFile in each year the annual aggregate exceeds $100,000 Shared property rules:

Each heir’s basis is their proportionate share of the stepped-up FMV on the date of death
If one heir buys out another, the purchasing heir adds the buyout price to their basis
Rental income from shared foreign property is split proportionally, and each heir reports their share on Schedule E
Sale proceeds are split per ownership share, and each heir reports their gain on their own Form 8949 and Schedule D

Example (3 siblings inherit a German property worth $600,000): ItemEach sibling’s shareStepped-up basis (1/3 of $600,000)$200,000Form 3520 reportingYes ($200,000 > $100,000)Sale proceeds (1/3 of $750,000)$250,000Capital gain per sibling$50,000Foreign tax credit per sibling1/3 of German tax paid Additional filings each heir may need:

FBAR: If you have signature authority over shared foreign bank accounts holding estate proceeds, and the aggregate of all your foreign accounts exceeds $10,000
Form 8938: If your share of inherited foreign financial assets puts you above the FATCA threshold
Form 1116: Each heir claims their proportional share of foreign taxes paid

For foreign inheritance reporting help, see our Foreign Inheritance Tax Guide.

Question 11

What Is the PFIC Mark-to-Market Election and When Should I Use It?

Accepted Answer

The mark-to-market (MTM) election under IRC Section 1296 lets you recognize gain or loss on a marketable PFIC each year based on the change in its fair market value from January 1 to December 31. This avoids the punitive Section 1291 excess distribution regime, which imposes top ordinary income rates plus compounding interest on deferred gains.

How the MTM election works:

Year-end value exceeds adjusted basis: You recognize ordinary income equal to the increase
Year-end value falls below adjusted basis: You recognize an ordinary loss, but only to the extent of prior MTM gains (net mark-to-market gain)
Basis adjusts annually: Increases by gains recognized, decreases by losses

YearYear-end FMVBasis (start)Gain/(Loss) recognizedNew basis2023$12,000$10,000$2,000 gain$12,0002024$11,000$12,000($1,000) loss$11,0002025$14,000$11,000$3,000 gain$14,000 Eligibility requirements:

Marketable stock only: The PFIC must be regularly traded on a qualifying exchange (NYSE, NASDAQ, LSE, TSX, ASX, and most national exchanges recognized by the IRS)
Non-traded funds do not qualify: Unlisted mutual funds, hedge funds, and private equity cannot use MTM
Election made on Form 8621: Attach to a timely filed return in the first year you want the election to apply

MTM vs. QEF vs. Section 1291: FeatureMTMQEFSection 1291Tax rateOrdinary incomeOrdinary + capital gainsTop ordinary + interestFund info neededMarket price onlyAnnual Information StatementNoneLoss deductibleLimited to prior gainsNo (but basis increases)NoBest forExchange-traded PFICsFunds providing AISLast resort When MTM is the right choice:

Your PFIC is exchange-traded, but the fund does not provide a QEF Annual Information Statement (common with foreign-listed ETFs)
You want simplicity: Just look up the December 31 price, no need to obtain fund-level income data
You missed the first-year QEF window: MTM can be elected in any year without a purging election (though prior-year Section 1291 taint on pre-MTM gain may still apply at sale)

For the PFIC election strategy, see our PFIC Reporting Guide.

Question 12

How Do I Bring Money to the U.S. After Selling Property Abroad?

Accepted Answer

There is no U.S. law preventing you from wiring the proceeds of a foreign property sale to a U.S. bank account. The transfer itself is not a taxable event. However, the capital gain on the sale is taxable on your U.S. return regardless of whether you bring the money home, and large transfers trigger bank reporting and may affect your FBAR and Form 8938 obligations.

What happens when you wire the money: AmountWhat gets triggeredAny amountCapital gain is already taxable on Form 1040 in the year of saleWire over $10,000 received by a U.S. bankBank files Currency Transaction Report (CTR) automaticallyAggregate foreign accounts over $10,000 at any point in the yearFBAR (FinCEN 114)Foreign financial assets above FATCA thresholdsForm 8938 Common misconceptions:

“I only owe tax when I bring the money to the U.S.”: Wrong. U.S. citizens and green card holders owe tax on worldwide income in the year it is earned, not when it is repatriated
“The wire transfer is taxed”: Wrong. The wire itself is not income. The taxable event was the property sale
“I need to report the wire to the IRS”: Not directly, but the receiving bank may file a CTR, and large foreign account balances in the year of sale often push you above FBAR and FATCA thresholds

Practical steps for a smooth transfer:

Notify your U.S. bank before sending a large international wire to avoid holds or account freezes
Keep closing documents: Sale contract, notary records, wire confirmations, and exchange rate documentation
File FBAR if the foreign account holding proceeds (even briefly) caused your aggregate foreign accounts to exceed $10,000 at any point during the year
Claim the Foreign Tax Credit on Form 1116 for any foreign capital gains tax paid on the sale

For foreign property sale tax planning, see our Buying and Selling Real Estate Abroad.

Question 13

Can I Claim Depreciation on My Foreign Rental Property for U.S. Tax Purposes?

Accepted Answer

Yes, you can and must claim depreciation on a foreign rental property on your U.S. return. For foreign residential rental property, use the Alternative Depreciation System (ADS) with a 30-year straight-line recovery period for property placed in service after 2017. Commercial foreign property uses a 40-year ADS period. This is different from the 27.5-year MACRS schedule used for domestic residential rentals.

ADS depreciation rules for foreign property: Property typeRecovery periodMethodResidential rental (post-2017)30 yearsStraight-lineResidential rental (pre-2018)40 yearsStraight-lineCommercial (all years)40 yearsStraight-line How to calculate your annual deduction:

Start with the building’s cost basis in USD (purchase price minus land value, converted at purchase-date exchange rate, plus allocable closing costs)
Subtract land value: Only the building depreciates. Use the local tax assessment ratio or an appraisal to split land vs. building
Divide by 30 (or 40): That is your annual straight-line deduction
Mid-month convention: In the first and last year, prorate by the month placed in service or disposed of

Example (UK rental, placed in service June 2023): ItemAmountTotal basis (USD)$500,000Land allocation (30%)($150,000)Depreciable building basis$350,000Annual ADS deduction (30 years)$11,667 Key points:

Depreciation is mandatory, not optional. If you fail to claim it, the IRS reduces your basis as if you did when you sell (depreciation recapture at 25% max rate)
Report on Form 4562 and flow through to Schedule E
Foreign tax credit: Depreciation reduces your U.S. taxable rental income, which can affect the FTC limitation on Form 1116
Bonus depreciation and Section 179 do not apply to foreign real property

For a full walkthrough, see our guide on How to Report Rental Income from Foreign Property.

Question 14

Are My Foreign Mutual Funds Considered PFICs for U.S. Tax Purposes?

Accepted Answer

Yes, most non-U.S. mutual funds, ETFs, UCITS funds, unit trusts, and other pooled investment vehicles are classified as Passive Foreign Investment Companies (PFICs) because they easily meet one of the two PFIC tests: 75% or more of gross income is passive (dividends, interest, capital gains), or 50% or more of assets are held for producing passive income. This triggers the filing of Form 8621 for each PFIC you hold every year.

Common foreign funds and PFIC status: Fund typeCountryPFIC?UCITS ETFs (e.g., Vanguard FTSE, iShares)Ireland, LuxembourgYesOEICs, unit trusts, investment trustsUKYesMutual funds, ETFs (e.g., BMO, RBC)CanadaYesManaged funds, super fundsAustraliaYesMutual funds (e.g., SBI, HDFC, ICICI)IndiaYesPEA-eligible fundsFranceYesU.S.-registered funds held in foreign accountAnyNo Why this catches so many expats by surprise:

Your foreign financial advisor typically recommends local funds without knowing U.S. PFIC rules
Employer pension schemes may hold underlying funds that are PFICs (e.g., UK workplace pension with OEIC sub-funds)
Even small holdings trigger Form 8621 filing; there is no de minimis exception
The default Section 1291 tax regime is punitive: top ordinary income rate plus compounding interest on deferred gains

How to check if your fund is a PFIC:

Is it organized outside the U.S.? If yes, apply the income and asset tests
Is it a pooled fund (mutual fund, ETF, unit trust)? If yes, it almost certainly passes the 75% passive income test
Is it registered with the SEC as a U.S. investment company? If yes, it is not a PFIC regardless of where you hold it

What to do if you hold foreign mutual funds:

File Form 8621 for each PFIC for each tax year held
Consider a QEF or mark-to-market election to avoid the punitive default regime
Restructure future investments into U.S.-registered funds or individual stocks where practical

For PFIC identification and filing help, see our PFIC Reporting Guide.