Chapter 4 is dedicated to the concept of informality as a crucial legal concept for the understanding of trilogues. It begins from a twofold observation. First, the informal nature of trilogues is stated in black and white in a significant variety of legal instruments. Secondly, the role of legal scholarship is to make sense of that unequivocal characterization. Drawing on institutional theory, this chapter argues that informality is a full-blown concept of EU law, and it sets about defining its characteristics. To that end, it compares trilogues with two other informal bodies, namely the Euro Group and the Informal Council meetings. The core idea of this chapter is that the codification of informality translates into legal terms the intention of the institutions to protect certain spaces from an excessive penetration of legal normativity. This intention, in turn, is indicative of the desire to preserve those spaces for the emergence of powerful social frameworks where genuine exchanges among actors may occur; exchanges that should be conducive to compromise.