The key component to matching target users across mobile and desktop is some form of authenticated connection and both Facebook and Google have this. While Facebook has been leveraging its user base for a while with its Atlas ad server Google is joining the party by allowing its DoubleClick ad service do the same.
Google has more authenticated users than marketers may think because if a user logs into any Google service, be it YouTube, Gmail, Chrome, or even Google+ that user then has a cross-service Google ID that can be identified by DoubleClick.
As well as the cross-device tracking announcement, DoubleClick claims that it can compare its results to competing ad services:
In another competitive signal to the market, Google has announced that the DoubleClick cross-device measurement tool will allow marketers to measure all their campaigns across the web – not just the ads it books with Google – so they can see how their campaigns using different servers stack up.
Source: Business Insider