大萧条(Great Depression)，亦称1929年萧条（Depression of 1929）。
西方世界所经历的时间最长和最严重的经济萧条。开始於在美国纽约发生的1929年股市大崩盘，持续至1939年左右。到1932年末，股价跌到只有之前市值的20%左右；而到1933年，美国25,000家银行中有11,000家宣告破产，导致需求和产出水平大大下降，造成高失业率（至1932年失业率达25～30%）。由於美国是战後欧洲的主要债权人和资金融通者，一旦美国经济陷入萧条，欧洲的繁荣随之崩溃，特别是德国和英国。各国均藉由提高关税、对外贸进口规定配额来保护自己国内的贸易。到1932年，世界贸易总值减少一半以上。大萧条在政治领域也产生了重大的後果。在美国，经济危机导致罗斯福当选为总统，他的新政对美国的经济结构造成若干重大变革。在德国，经济灾难直接导致了希特勒的崛起，於1933年夺取政权。在欧洲其他国家，大萧条增强了极端主义势力，降低了自由民主的威望。在大萧条以前，各国政府依赖客观的市场力量去获致必要的经济纠正；而在大萧条以後，政府开始承担主要的作用，以确保经济稳定。
English version：
Great Depression
Longest and most severe economic depression ever experienced by the Western world. It began in the U.S. with the New York Stock Market Crash of 1929 and lasted until about 1939. By late 1932 stock values had dropped to about 20% of their previous value, and by 1933 11,000 of the U.S.'s 25,000 banks had failed. This led to much-reduced levels of demand and hence of production, resulting in high unemployment (by 1932, 25-30%). Since the U.S. was the major creditor and financier of postwar Europe, the U.S. financial collapse led to collapses of other economies, especially those of Germany and Britain. Nations sought to protect domestic production by imposing tariffs and quotas, reducing the value of international trade by more than half by 1932. The Great Depression contributed to political upheaval. It led to the election of Franklin Roosevelt in the U.S. and major changes in the structure of the U.S. economy brought about by his New Deal. It directly contributed to Adolf Hitler's rise to power in Germany in 1933 and to political extremism in other countries. Before the Great Depression, governments relied on impersonal market forces to achieve economic correction; afterward, government action came to assume a principal role in ensuring economic stability.