Datalog is a declarative logic programming language, which has in recent years found new uses as a graph query language in server and client applications. This talk introduces Datalog from its primitives and builds a mental model of how complicated queries can be resolved using simple data structures. This, in turn, will help you understand when and how you should apply Datalog in practice: on the client, on the server, as a graph database, as a communication protocol ala GraphQL/Falcor, or as an event-sourcing storage mechanism.