The SMT-LIB initiative is an international effort, supported by research groups worldwide, with the two-fold goal of producing an extensive on-line library of benchmarks and promoting the adoption of common languages and interfaces for SMT solvers. This paper introduces Version 2 of the SMT-LIB Standard. This is a major upgrade of the previous Version 1.2 which, in addition to simplifying and extending the languages of that version, includes a new command language for interfacing with SMT solvers.