Tax evasion is the illegal evasion of taxes by individuals, corporations, and trusts. Tax evasion often entails taxpayers deliberately misrepresenting the true state of their affairs to the tax authorities to reduce their tax liability and includes dishonest tax reporting, such as declaring less income, profits or gains than the amounts actually earned, or overstating deductions.

Tax evasion is an activity commonly associated with the informal economy. One measure of the extent of tax evasion (the "tax gap") is the amount of unreported income, which is the difference between the amount of income that should be reported to the tax authorities and the actual amount reported.

In contrast, tax avoidance is the legal use of tax laws to reduce one's tax burden. Both tax evasion and avoidance can be viewed as forms of tax noncompliance, as they describe a range of activities that intend to subvert a state's tax system, although such classification of tax avoidance is not indisputable, given that avoidance is lawful, within self-creating systems.