Eight companies wield enormous power over the entire internet: Google, Facebook, Microsoft, Amazon, Apple, Baidu, Alibaba and Tencent. Most internet users today are in daily contact with at least one. They each have so many different products, services and investments that it’s not always clear what their main source of revenue is, or how a company profits from services offered for “free,” such as search, email, games, social media or instant messaging.

Just how do these giants of the internet make money? We’ve sorted them into four overlapping categories according to their primary source of revenue.