What was the codename for Windows Vista?

The codename for Windows Vista was Longhorn. Microsoft began developing the project in 2001, originally planning it as a relatively small successor to Windows XP that would sit between XP, codenamed Whistler, and a larger future release called Blackcomb.

The project grew substantially as Microsoft added technologies and features intended for Blackcomb, including new presentation, communications, and storage systems. This expansion caused major delays and led Microsoft to reset development in 2004 using a more stable Windows Server 2003 code base. The project continued under the Longhorn name during much of its pre-release period.

Microsoft officially announced the name Windows Vista in July 2005, and the operating system was released to manufacturing on November 8, 2006. Longhorn was named after the Longhorn Bar at the Whistler Blackcomb ski resort in British Columbia, reflecting the planned position between the Whistler and Blackcomb codenames. Blackcomb and Whistler therefore belong to related Windows projects, but neither was Vista's codename.