1. A computer-implemented method comprising: accessing, by a computer system, a search history that identifies one or more search queries that were previously submitted to one or more search services by a mobile computing device that is associated with a user; accessing information that identifies one or more web pages that were previously displayed on the mobile computing device; identifying, based at least in part on i) the search history of the mobile computing device, ii) search results associated with the one or more search queries in the search history, and iii) content included in the one or more web pages that were previously displayed on the mobile computing device, a geographic location to which future voice input from the user is likely to relate; selecting, by the computer system and based at least in part on the identified geographic location, a first grammar from among a plurality of grammars, wherein the first grammar includes a vocabulary that is relevant to the identified geographic location; and outputting, by the computer system, information that identifies the first grammar, wherein the outputted information causes a grammar used to analyze voice input from the mobile computing device to be changed to the first grammar.