BBC Sport looks back at some of the best mid-season transfers and how they changed the clubs' Premier League fortunes.
Luis Suarez's January transfer to Liverpool in 2011 features, as does West Ham's double signing of Paul Kitson and John Hartson and Birmingham's inspired signing of Christophe Dugarry.
The transfer window closes at 23:00 GMT on Friday 31 January, and you can find out how to follow the latest developments across BBC Sport here.
Pictures courtesy of the Premier League.
Available to UK users only.