"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.

Stewart Brett McKinney was an American politician of the Republican Party who represented Connecticut's 4th congressional district in the House of Representatives from 1971 until his death. He is perhaps best known for coining the phrase "too big to fail" in regard to large American financial institutions, as well as for his struggle with, and eventual death from, AIDS.