The DoubleClick side of the business still exists: it's called Google AdManager. Very roughly, AdSense is "hey Google, please put ads on my page and make me mon

The DoubleClick side of the business still exists: it's called Google AdManager. Very roughly, AdSense is "hey Google, please put ads on my page and make me money" while AdManager is "I'm a big publisher and make deals directly with advertisers for most of the ads I show". AdSense was built internally, DoubleClick was an acquisition. (Disclosure: I work on ads at Google, speaking only for myself)