Double taxation is the levying of tax by two or more jurisdictions on the same income (in the case of income taxes), asset (in the case of capital taxes), or financial transaction (in the case of sales taxes).

Double liability may be mitigated in a number of ways, for example, a jurisdiction may:

Jurisdictions may enter into tax treaties with other countries, which set out rules to avoid double taxation. These treaties often include arrangements for exchange of information to prevent tax evasion – such as when a person claims tax exemption in one country on the basis of non-residence in that country, but then does not declare it as foreign income in the other country; or who claims local tax relief on a foreign tax deduction at source that had not actually happened.

The term "double taxation" can also refer to the taxation of some income or activity twice. For example, corporate profits may be taxed first when earned by the corporation (corporation tax) and again when the profits are distributed to shareholders as a dividend or other distribution (dividend tax).

There are two types of double taxation: jurisdictional double taxation, and economic double taxation. In the first one, when source rule overlaps, tax is imposed by two or more countries as per their domestic laws in respect of the same transaction, income arises or deemed to arise in their respective jurisdictions. In the latter one, when same transaction, item of income or capital is taxed in two or more states but in hands of different person, double taxation arises.

It is not unusual for a business or individual who is resident in one country to make a taxable gain (earnings, profits) in another country. It could happen that a person will need to pay tax on that income locally and also in the country in which it was made. The stated goals for entering into a treaty often include reduction of double taxation, eliminating tax evasion, and encouraging cross-border trade efficiency. It is generally accepted that tax treaties improve certainty for taxpayers and tax authorities in their international dealings.

A DTA (double tax agreement) may require tax to be levied by the country of residence, and be exempt in the country in which it arises. In other cases, the resident may pay a withholding tax to the country where the income arose, and the taxpayer receives a compensating foreign tax credit in the country of residence to reflect the fact that tax has already been paid. In the former case, the taxpayer would declare himself (in the foreign country) a non-resident. In either case, the DTA may provide that the two taxation authorities exchange information about such declarations. Because of this communication between the countries, they also have a better view on individuals and companies who are trying to avoid or evade tax.

South Africa maintains double taxation agreements (DTAs) with several countries, offering relief mechanisms such as tax credits and exemptions for foreign income.