Bulletin No. 257, article 4. In response to the 2007-09 financial crisis, supervisory authorities reinforced bank stress tests, with the aim of safeguarding financial stability. The implementation of these tests differs in Europe and the United States. European tests cover all large and medium-sized banks. They are carried out by the banks themselves using their own internal methods under constrained rules, and the results are verified and validated by the supervisor. US tests are carried out on smaller samples of the largest banks, using models developed by the supervisor.