Windows Azure is the name of the upcoming cloud-based operating system being developed by Microsoft, announced by Ray Ozzie at the Microsoft PDC on October 27, 2008. It is the operating system that will host the Azure Services Platform. It was pre-announced as "Windows Cloud" at a Microsoft Student Technology Day on October 1, 2008 by Steve Ballmer.^[1][2] Windows Azure forms the operating system which will host the Azure Services Platform.

According to Steve Ballmer, Windows Azure is to be based on Windows Server, with features including geo replication, network management model, and a SOA model.