MLS operates two transfer windows each season, aligned with FIFA regulations. The Primary Transfer Window typically runs from mid-February through early May, coinciding with the start of the MLS season. The Secondary Transfer Window opens in mid-July and closes in mid-August, providing a mid-season opportunity to strengthen rosters.
Outside these windows, MLS teams cannot register new players from other leagues, though intra-league trades and certain roster moves (like signing free agents within MLS) may still be possible. The transfer windows create urgency in negotiations and strategic planning, as teams must finalize acquisitions within the defined periods. MLS roster freeze deadlines ahead of the playoffs add another layer of planning for contending teams.