| Term | Definition / Meaning / Stand for |
| ILR |
Immigration Levy Return (tax-related) |
| IRPEF |
Imposta sul Reddito delle Persone Fisiche (Italian individual tax) |
| ICMS |
Imposto sobre Circulação de Mercadorias e Serviços (Brazilian goods tax) |
| IEPS |
Impuesto Especial sobre Producción y Servicios (Mexican excise tax) |
| IVA |
Impuesto al Valor Agregado (VAT in Spanish-speaking countries) |
| ISF |
Impuesto sobre la Renta de las Personas Físicas (Spanish individual income tax) |
| IDG |
Income Distribution Group (tax projection) |
| IFS |
Income Forecast Scheme |
| IPG |
Income Projection Guide |
| ICTA |
Income and Corporation Taxes Act |
| IRD |
Income in Respect of a Decedent |
| IDT |
Indirect Tax |
| IIT |
Individual Income Tax |
| IHT |
Inheritance Tax |
| IRET |
Institute for Research on the Economics of Taxation |
| IPT |
Insurance Premium Tax |
| IFA |
Intangible Fixed Assets (with tax implications) |
| IC-DISC |
Interest Charge-Domestic International Sales Corporation |
| IDWT |
Interest and Dividends Withholding Tax |
| IGT |
Intergenerational Transfer (tax-related) |
| IBT |
International Business Tax |
| ICS |
International Corporate Structure (with tax implications) |
| ICTA |
International Corporate Tax Agreement |
| IFT |
International Financial Transaction (tax reporting) |
| IHR |
International Harmonized Rates (of tax) |
| IHC |
International Holding Company (with tax incentives) |
| IGR |
Investment Growth Rate (tax-related) |
| IPRS |
Investment Property Reporting System (tax-related) |
| IRB |
Investment Research Board (with tax implications) |
| ITE |
Investment Tax Exemption |
| IUB |
Investment Unit Benefit (tax projection) |
| IVR |
Investment Valuation Report (tax-related) |
| ILIT |
Irrevocable Life Insurance Trust (estate tax purposes) |
| ISO |
Incentive Stock Option (tax treatment) |
| ITA |
Income Tax Act |
| ITR |
Income Tax Return |
| INC |
Incorporated (with corporate tax implications) |
| INR |
Indian National Rupee (currency for tax-related transactions) |
| IRA |
Individual Retirement Account (tax-deferred savings) |
| ITIN |
Individual Taxpayer Identification Number |
| ICT |
Information and Communication Technology (tax-related benefits) |
| IPO |
Initial Public Offering (with tax implications) |
| IP |
Intellectual Property (taxation in transfers and licensing) |
| IBOR |
Interbank Offered Rate (affects tax on investments) |
| IGA |
Intergovernmental Agreement (with tax consequences) |
| IRC |
Internal Revenue Code |
| IRS |
Internal Revenue Service |
| IATA |
International Air Transport Association (tax-related fees) |
| IBFD |
International Bureau of Fiscal Documentation |
| IFRS |
International Financial Reporting Standards (affect tax reporting) |
| IMF |
International Monetary Fund (with tax-related programs) |
| ITC |
Investment Tax Credit |