You could think of Cortana as Microsoft Now. We Android users ask Google questions by default, but when you’re on a modern Windows device, Cortana’s the one who will chime in with an answer.
Microsoft’s plans to bring Cortana to Android has been no secret.
[Update: US And China Only] Cortana Exits Public Beta And Is Now Officially Available For Android was written by the awesome team at Android Police.
Source: Andriod Police