International taxation is the study or determination of tax on a person or business subject to the tax laws of different countries, or the international aspects of an individual country's tax laws as the case may be. Governments usually limit the scope of their income taxation in some manner territorially or provide for offsets to taxation relating to extraterritorial income. The manner of limitation generally takes the form of a territorial, residence-based, or exclusionary system. Some governments have attempted to mitigate the differing limitations of each of these three broad systems by enacting a hybrid system with characteristics of two or more.

Many governments tax individuals and/or enterprises on income. Such systems of taxation vary widely, and there are no broad general rules. These variations create the potential for double taxation (where the same income is taxed by different countries) and no taxation (where income is not taxed by any country). Income tax systems may impose tax on local income only or on worldwide income. Generally, where worldwide income is taxed, reductions of tax or foreign credits are provided for taxes paid to other jurisdictions. Limits are almost universally imposed on such credits. Multinational corporations usually employ international tax specialists, a specialty among both lawyers and accountants, to decrease their worldwide tax liabilities.

With any system of taxation, it is possible to shift or recharacterize income in a manner that reduces taxation. Jurisdictions often impose rules relating to shifting income among commonly controlled parties, often referred to as transfer pricing rules. Residency-based systems are subject to taxpayer attempts to defer recognition of income through use of related parties. A few jurisdictions impose rules limiting such deferral ("anti-deferral" regimes). Deferral is also specifically authorized by some governments for particular social purposes or other grounds. Agreements among governments (treaties) often attempt to determine who should be entitled to tax what. Most tax treaties provide for at least a skeleton mechanism for resolution of disputes between the parties.