Online advertising uses all kinds of machine learning. When companies are running billions of impressions across multiple ad networks and using different creat

Online advertising uses all kinds of machine learning. When companies are running billions of impressions across multiple ad networks and using different creative variants, it takes serious algorithms to cut through the noise and find the inventory that's performing well. It's a tricky problem because typically you'll get tiny click-through rates, meaning you're looking to group a few points of data among millions of impressions. Contextual analysis (figuring out the context of the page where the ad appears) is a big deal now also. That's a lot of natural language processing on some of the most diverse (read: difficult) content available. I happen to work for a company that does both of these. :)