Tax evasion is an illegal attempt to defeat the imposition of taxes by individuals, corporations, trusts, and others. Tax evasion often entails the deliberate misrepresentation of the taxpayer's affairs to the tax authorities to reduce the taxpayer's tax liability, and it includes dishonest tax reporting, declaring less income, profits or gains than the amounts actually earned, overstating deductions, using bribes against authorities in countries with high corruption rates and hiding money in secret locations.

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 tax 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, but such classification of tax avoidance is disputable since avoidance is lawful in self-creating systems. Both tax evasion and tax avoidance can be practiced by corporations, trusts, or individuals.