Cortana is an intelligent virtual assistant for the Windows Phone 8.1 operating system, available on an opt-in basis.

Its name comes from Cortana, the artificial intelligence from the Halo series, with Jen Taylor, the voice actress for the character, lending her voice to the personal assistant.

Cortana was first demonstrated by Microsoft Corporate Vice President Joe Belfiore at the Microsoft BUILD Developer Conference (April 2-4, 2014) in San Francisco, United States.

It was launched as a key ingredient in Microsoft's planned "overhaul" of future operating systems for Windows Phone, Windows, and Xbox One.

On January 21, 2015, Microsoft announced the arrival of Cortana for computers running Windows 10.