The PREFAB project aims to identify and analyze the prefabricated patterns of French interactions (e.g. comment dirais-je ‘how shall I put it’), in spoken corpora, interactional written corpora, and dialogues in fiction (these resources are already available). The project, initiated by LIDILEM, integrates researchers from ICAR, ATILF and BCL, research units with complementary skills. The modeling is based on construction grammars and includes syntactic, semantic, pragmatic and interactional dimensions. The innovative aspects of the project are : (a) the study of a very wide range of prefabricated patterns, from expressive expressions to metadiscursive patterns (b) an integrated approach to levels of linguistic processing (in a model based on "constructicons") (c) an innovative inductive methodology of corpus exploration (including treebanks) (d) the study of variation between sub-genres and mediums, including a comparison between French and German c. The data compiled will be freely available. They will contribute to the linguistic heritage and will be useful for language teaching as well as computer applications.