"Too big to fail" (TBTF) is a theory in banking and finance that asserts that certain corporations, particularly financial institutions, are so large and so interconnected that their failure would be disastrous to the greater economic system, and therefore should be supported by government when they face potential failure. The colloquial term "too big to fail" was popularized by U.S. Congressman Stewart McKinney in a 1984 Congressional hearing, discussing the Federal Deposit Insurance Corporation's intervention with Continental Illinois. The term had previously been used occasionally in the press, and similar thinking had motivated earlier bank bailouts.

The term emerged as prominent in public discourse following the global financial crisis of 2007–2008. Critics see the policy as counterproductive and that large banks or other institutions should be left to fail if their risk management is not effective. Some critics, such as economist Alan Greenspan, believe that such large organizations should be deliberately broken up: "If they're too big to fail, they're too big." Some economists such as Paul Krugman hold that financial crises arise principally from banks being under-regulated rather than their size, using the widespread collapse of small banks in the Great Depression to illustrate this argument.

In 2014, the International Monetary Fund and others said the problem still had not been dealt with. While the individual components of the new regulation for systemically important banks (additional capital requirements, enhanced supervision and resolution regimes) likely reduced the prevalence of TBTF, the fact that there is a definite list of systemically important banks considered TBTF has a partly offsetting impact.