Law No 2004-391 of 4 May 2004 made it possible to negotiate collective agreements (in particular at company level) derogating in pejus from agreements covering a broader professional or territorial scope (branch agreements, inter-branch agreements, etc.), provided that the latter do not prohibit such derogations. The purpose of this study is to assess the implementation of this possibility of derogation on the basis of monographs of undertakings and conventional branches. Noting that, over the period 2004-2007, the number of agreements deemed to be derogatory within the meaning of the Law of 4 May 2004 was insignificant, the authors were led to focus the analysis on the reasons for not using the possibility of signing derogation agreements at the level of undertakings. The complexity perceived as excessive in the new legal framework, the inadequacy of the system in the light of the practices and challenges of collective bargaining in companies, the existence of strong legal uncertainty as to the concept of derogation, and the lock-in of the scheme by the parties involved in the conventional branches, are all identified reasons for the non-use of the option to derogate. More broadly, it is the question of the articulation of levels of collective bargaining that is reconsidered in the study, as the derogating and more or less favourable nature of one collective agreement compared to another is in many cases difficult to establish. Finally, a paradoxical effect of the possibility of signing derogation agreements in companies is to have led industry players to reaffirm their willingness to retain control over the definition of certain elements of employees’ employment status, by introducing restrictive clauses in the new collective agreements. The legal analysis of the multiple formulations used in branch agreements to restrict trading margins at company level thus reveals the high degree of complexity achieved in the articulation of standard agreements.