A system and method is provided to track users across applications and devices, and to distinguish similar or different users among a number of commonly-used devices. Accordingly, systems and methods are provided for analyzing user device information to determine different users among a number of devices. In particular, user's behavior when using the devices is observed, and responsive to that observed behavior, is the determined whether a particular users are distinguishable from other users. For instance, it may be useful to distinguish between users that operate the same devices or exist within a similar network (e.g., a home network, a workplace network, etc.) for various purposes. For instance, it may be useful to distinguish between users for displaying advertising to these users, performing some other operation with respect to a subset of the users.