An information system is a primitive structure that defines which agents can initially get information and how such information is then distributed to others. From political and organizational economics to privacy, information systems arise in various contexts and, unlike information itself, can be easily observed empirically. We introduce a methodology to characterize how information systems affect strategic behavior. This involves proving a revelation principle result for a novel class of constrained information design problems. We identify when such systems better distribute information and, as a result, impose more constraints on behavior. This leads to a novel notion of an agent's influence in the system. Finally, we apply our theory to examine how current patterns of news consumption from mass media may affect elections.