We present Frigram, a French grammar with a large coverage, written in the formalism of Interaction Grammars. The originality of the formalism lies in its system of polarities, which expresses the resource sensitivity of natural languages and which is used to guide syntactic composition. We focus the presentation on the principles of the grammar, its modular architecture, the link with a lexicon independent of the formalism and the companion property, which helps to guarantee the consistency of the whole grammar.