Gross v. FBL Financial Services, Inc., 557 U.S. 167 (2009), was a case decided by the Supreme Court of the United States in 2009, involving the standard of proof required for a claim under the Age Discrimination in Employment Act (ADEA).

Jack Gross, an employee of FBL Financial Services, Inc., was transferred to another position and a former subordinate took on many of Gross' old responsibilities. They both received the same compensation, but Gross believed his reassignment was a demotion. Gross brought suit against FBL in April 2004 in District Court, claiming ADEA violations. The court found in his favor and awarded him $5,000,000 in lost compensation. The United States Court of Appeals for the Eighth Circuit reversed the decision. The Supreme Court affirmed that reversal, finding that a plaintiff must prove by preponderance of evidence, that age was the "but for" cause of the adverse employment action.