Smart billboards around the country will bring Cortana to life, using weather, travel, location, business and events data to demonstrate her abilities in real time.
That ever-changing data means there are 9,640 variations on the creative for some 241 posters around the UK. The campaign runs until 18 June.
Microsoft marketing director Paul Davies said: "Just like Cortana, this campaign is personal, flexible, and hyper relevant to the context against which the ads are served, using location, date and time data.
"We have used digital technology as a creative canvas to showcase how Cortana helps people manage everyday life seamlessly and in a powerful way."
Agencies: Dentsu Aegis Network, M:United McCann, LivePoster