Online advertisements are often measured (and paid for) in terms of clicks. Companies usually buy ads at CPMs (or cost per thousand clicks). But publishers are starting to turn to engagement advertising, which focuses on the level of engagement with a product or ad rather than the number of click-throughs. It remains difficult, however, to measure engagement, and the industry has traditionally relied upon time as the measure. There are still obstacles to overcome, but industry experts expect engagement ads to be the future of online advertising.