In the United States, scheduled presidential transitions, those not brought about by a president’s death or resignation from office, begin the day after the November presidential election, and conclude roughly two and a half months later, on January 20, as specified in the Twentieth Amendment. The presidential transition is regulated by The Presidential Transition Act of 1963 Pub.L. 88–277, amended by The Presidential Transitions Effectiveness Act of 1998 Pub.L. 100–398  and The Presidential Transition Act of 2000 Pub.L. 106–293. The Act as amended directs the Administrator of General Services to provide facilities, funding of approximately five million dollars, access to government services, and support for a transition team, and to provide training and orientation of new government personnel and other procedures to ensure an orderly transition.
The president-elect will also usually appoint a ‘presidential transition team’ during the campaign to prepare for a smooth transfer of power following the presidential inauguration. A law enacted by the United States Congress in 2016 requires the incumbent President to establish “transition councils” by June of an election year to facilitate the eventual handover of power.
what exactly IS a transition team