Chelsea will be able to sign players during the January transfer window after CAS lifted their embargo.
The Blues took their appeal against a two-window transfer ban to the Court of Arbitration for Sport after Fifa handed down their sanction last February.
Fifa found the London club guilty of breaching article 19 of its regulations on the status and transfer of players (RSTP), which concerns the protection of minors.
CAS reviewed evidence from the Premier League club and world football's governing body and determined that the ban should be reduced.
Frank Lampard has previously indicated he will look to strengthen his squad in January - with Ben Chilwell, Wilfried Zaha and Jadon Sancho among the names linked with the Blues.
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