The subprime mortgage crisis is an ongoing economic problem that became more apparent during 2007 and 2008, and is characterized by contracted liquidity in the global credit markets and banking system. The downturn in the U.S. housing market, risky lending and borrowing practices, and excessive individual and corporate debt levels have caused multiple adverse effects on the world economy. The crisis has passed through various stages, exposing pervasive weaknesses in the global financial system and regulatory framework.

The crisis began with the bursting of the United States housing bubble and high default rates on "subprime" and adjustable rate mortgages (ARM), beginning in approximately 2005–2006. For a number of years prior to that, declining lending standards, an increase in loan incentives such as easy initial terms, and a long-term trend of rising housing prices had encouraged borrowers to assume difficult mortgages in the belief they would be able to quickly refinance at more favorable terms. However, once interest rates began to rise and housing prices started to drop moderately in 20062007 in many parts of the U.S., refinancing became more difficult. Defaults and foreclosure activity increased dramatically as easy initial terms expired, home prices failed to go up as anticipated, and ARM interest rates reset higher. Foreclosures accelerated in the United States in late 2006 and triggered a global financial crisis through 2007 and 2008. During 2007, nearly 1.3 million U.S. housing properties were subject to foreclosure activity, up 79% from 2006.

Major banks and other financial institutions around the world have reported losses of approximately US$435 billion as of 17 July 2008. In addition, the ability of corporations to obtain funds through the issuance of commercial paper was affected. This aspect of the crisis is consistent with a credit crunch. The liquidity concerns drove central banks around the world to intervene by bailing out defaulting financial corporations in order to encourage lending to worthy borrowers at the expense of tax payers.

The risks to the broader economy created by the financial market crisis and housing market downturn were primary factors in several decisions by the U.S. Federal Reserve to cut interest rates and the economic stimulus package passed by Congress and signed by President George W. Bush on February 13, 2008. Following a series of ad-hoc market interventions to bail out particular firms, a $700 billion proposal was presented to the U.S. Congress in September, 2008. These actions are designed to stimulate economic growth and inspire confidence in the financial markets. On 3 October 2008, the amended version of the bill was signed into law.