Digital advertising revenue in the U.S. surged to a record $40.1 billion in the first six months of the year, with mobile accounting for more than half of the advertising spend, according to a new industry trade group report.

The IAB: Interactive Advertising Bureau reported that digital ad revenues rose 23% from the same time a year ago, when brands and marketers spent $32.7 billion. In fact, the industry has quadrupled in size over the last decade.

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Mobile devices have emerged as the web’s leading ad format, with advertisers spending $21.7 billion on mobile ads during the first half of the year — a substantial 40% bump from a year ago. Ubiquitous smartphones have allowed advertisers to reach consumers virtually anywhere.

Social media platforms and digital video are also major drivers of growth. Advertising on social media platforms reached $9.5 billion, up a whopping 37% from a year ago. Digital video, on mobile devices and the computer desktop, rose to $5.2, a gain of 36% from the comparable period last year.

“We’ve seen digital marketing revenues climb steadily and this new analysis shows that there are more opportunities to be mined,” said Chris Kuist, SVP Research and Impact for IAB.

Here’s how advertising breaks down:

IAB: Internet Advertising Report For First Half of 2017
IAB: Interactive Advertising Bureau