Metamodeling is raising more and more interest in the field of language engineering. While this approach is now well understood for defining abstract syntaxes, formally defining concrete syntaxes with metamodels is still a challenge. Concrete syntaxes are traditionally expressed with rules, conforming to EBNF-like grammars, which can be processed by compiler compilers to generate parsers. Unfortunately, these generated parsers produce concrete syntax trees, leaving a gap with the abstract syntax defined by metamodels, and further ad-hoc hand-coding is required. In this paper we propose a new kind of specification for concrete syntaxes, which takes advantage of metamodels to generate fully operational tools (such as parsers or text generators). The principle is to map abstract syntaxes to concrete syntaxes via bidirectional mapping-models with support for both model-to-text, and text-to-model transformations.