[From Summary] The threshold issue in any Americans with Disabilities Act (ADA) case is whether the individual alleging discrimination is an individual with a disability. The ADA definition is a functional one and does not list specific disabilities. It defines the term disability with respect to an individual as "(A) a physical or mental impairment that substantially limits one or more of the major life activities of such individual; (B) a record of such an impairment; or (C) being regarded as having such an impairment." The Supreme Court in the landmark decision of Sutton v. United Air Lines examined the definition of disability used in the ADA and found that the determination of whether an individual is disabled should be made with reference to measures that mitigate the individual's impairment. This holding and related ones in other Supreme Court decisions have spawned new issues regarding the definition of disability in recent lower court cases. This report will briefly discuss the Supreme Court's opinions and analyze how the lower courts are interpreting the Supreme Court's holdings. It will be updated as appropriate.