Most of us do not realize the fact that inspite of it being free to users, Facebook is one of the biggest revenue earners in advertising in the world right now.
With a company that is worth over $100 Billion, it is surprising actually to find out that facebook earns almost $1 Billion per quarters in advertising revenue when it has more than 1.2 Billion 'free' active users on a monthly basis.
Facebook skillfully uses the information that users share on their profile to target them with ads that they would actually want to click on.
Also, facebook earns over $186 Million from games that it hosts by selling credits to the players addicted to such games like Farmville, Candy Crush Saga and the like.