Abstract: A social networking system provides instructions to third-party application developers for inclusion in applications. When executed, the instructions communicate information from an application to the social networking system describing user interactions with the application. Based on received information describing a user's interaction with an application, the social networking system determines likelihoods of the user performing various types interactions with applications and classifies the user based on the determined likelihoods. A user's interactions with additional applications similar to an application may be used to determine the likelihoods of the user performing different types of interactions with the application. Classifications associated with users may be used as targeting criteria for advertisements, allowing advertisers to target advertisements to users having a threshold likelihood of performing certain types of interactions with an application.