Menhir is a parser generator. It turns high-level grammar specifications, decorated with semantic actions expressed in the OCaml programming language, into parsers, again expressed in OCaml. It is based on Knuth's LR(1) parser construction technique. It is strongly inspired by its precursors: yacc, ML-Yacc, and ocamlyacc, but offers a large number of minor and major improvements that make it a more modern tool.