Applied computing is fundamentally a problem of languages, both natural and artificial. At least five languages mediate every interaction that we have with computers: first, the machine instruction sets, which are a prerequisite for all stored-program computing; second, the higher-level programming languages, which allow us to direct computation at a conceptual level; third, the algorithms, data structures, and “ontologies,” which give processes and objects of the world their computational representation; fourth, the visual and gestural languages of user interfaces, which open up computing to non-specialists; and fifth, the innovations in natural language that we humans need in order to talk to each other about machines with unprecedented capabilities and behaviors.