The FAA applies to an arbitration agreement between defendant, a paratransit provider, and plaintiff, one of its drivers. Though plaintiff was not an employer “in” interstate commerce since he drove only local, in-state routes not necessarily connected to airports or other modes of interstate commerce, his employer provided paratransit services mandated by the ADA. Plaintiff was hired to and did provide those services. And those paratransit services facilitated further commercial activity by the passengers who used the services. The ADA was enacted under Congress’ Commerce Clause powers, and Congress determined that prohibiting discrimination against the disabled facilitated their involvement in interstate commerce.