Chapter 1 is devoted to the history of trilogues, tracing their origins and showing why they were created and how they have changed over time. In particular, the chapter highlights that trilogues have characterized the "European way" of adopting legislation since 1975, when the Parliament attained its first competences in budgetary matters and successfully advocated for the establishment of a conciliation procedure. The establishment of this procedure, which bears striking similarities to today’s trilogues, should be regarded as a “critical juncture.” It set a specific trajectory of institutional development and consolidation that has significantly shaped legislative interactions up to the present day, especially in the wake of subsequent Treaty amendments that have increasingly placed the three institutions in a relationship of mutual dependence.

Chapter 3 reconstructs the functioning of the European legislative process in practice. To this end, it systematizes the main normative instruments that steer and discipline the behavior of European political actors and civil servants, including the (rather bare) Treaty provisions, the relevant interinstitutional agreements, the European Parliament’s Rules of Procedure, and the provisions set out in internal documents, especially administrative circulars. This chapter posits that administrative circulars are important for institutional interactions, as they contribute to regularizing the conduct of political actors (regulative component), creating normative expectations (normative component), and generating values, beliefs, and assumptions that actors internalize and accept as part of their “repertoire of unquestioned routines and habits” (cultural-cognitive component). As far as trilogues are concerned, all these provisions testify to the existence of a norms-based, institutionalized environment, congenial to legal analysis.