There are two transfer windows in each Barclays Premier League season.
The first commences at midnight on the last day of the season and ends on 31 August if a working day - or, if not, on the first working day thereafter, at a time determined by the Board.
The second transfer window commences at midnight on the 31 December and ends on the 31 January if a working day, and again, if not, on the first working day thereafter, at a time determined by the Board.
Temporary transfers can be made permanent outside of the transfer windows. For further information please see the rules in the Premier League Handbook.