The window opened at 00:01 on May 17th, and will run to 17:00 on August 9th - before the opening game of the 2018/19 season.
In previous years the window has closed at the end of August, and this had led to some tense standoffs between clubs and players as they have tried to force various moves.
Last season, Virgil van Dijk and Philippe Coutinho were the most famous cases. Both were not seen for their clubs in August as they attempted to engineer a move away, creating uncertainty and division that both sides would rather avoid. As it was both players got their move in January.
However, transfers from abroad can only be finalised once the FIFA Transfer Matching System (TMS) opens, which will be midnight on June 8th. Until then, while talks can be ongoing, only domestic transfers will be able to go through.
As it stands, the Premier League is forging its own path with these new dates, as the top leagues in France, Spain, Germany and Italy will all be retaining the August 31st finishing date.