A bank failure occurs when a bank is unable to meet its obligations to its depositors or other creditors because it has become insolvent or too illiquid to meet its liabilities. A bank usually fails economically when the market value of its assets declines to a value that is less than the market value of its liabilities. The insolvent bank either borrows from other solvent banks or sells its assets at a lower price than its market value to generate liquid money to pay its depositors on demand. The inability of the solvent banks to lend liquid money to the insolvent bank creates a bank panic among the depositors as more depositors try to take out cash deposits from the bank. As such, the bank is unable to fulfill the demands of all of its depositors on time. A bank may be taken over by the regulating government agency if its shareholders' equity are below the regulatory minimum.

A bank run or run on the bank occurs when many clients withdraw their money from a bank, because they believe the bank may fail in the near future. In other words, it is when, in a fractional-reserve banking system, numerous customers withdraw cash from deposit accounts with a financial institution at the same time because they believe that the financial institution is, or might become, insolvent. When they transfer funds to another institution, it may be characterized as a capital flight. As a bank run progresses, it may become a self-fulfilling prophecy: as more people withdraw cash, the likelihood of default increases, triggering further withdrawals. This can destabilize the bank to the point where it runs out of cash and thus faces sudden bankruptcy. To combat a bank run, a bank may acquire more cash from other banks or from the central bank, or limit the amount of cash customers may withdraw, either by imposing a hard limit or by scheduling quick deliveries of cash, encouraging high-return term deposits to reduce on-demand withdrawals or suspending withdrawals altogether.