The lochner era is a period in American legal history from roughly 1905 to 1937 where the United States Supreme Court made a series of judgements establishing a laissez-faire policy towards individual and group rights in favour of market self-regulation. During this period the court struck down a great deal of federal and state legislation designed to improve working conditions.

The eponymous 1905 case of Lochner v. New York was where the court struck down a law limiting the number of hours worked by bakers because it violated their "right to contract".

Other representative cases include Hammer v. Dagenhart (1918), where the court stuck down legislation aimed at reducing child labor in factories where children under 14 worked; as well as Adkins v. Children's Hospital (1923), where the court stuck down federal legislation that established a minimum wage level for women in D.C..

The era is considered to have ended with the overturning of Adkins v. Children's Hospital in the 1937 case of West Coast Hotel Co. v. Parrish.

Since that period the lochner era is generally considered by both liberals and conservatives alike to be a regrettable period in U.S. jurisprudence, each for different reasons. Liberal-minded people considered it a shameful time for workers' rights and conservatives use it as a example of the inappropriate judicial activism.

"Locherizing" has developed into a verb used in the legal community to denote judicial activism.