Every constitution needs to set out rules for the production of its laws. Legislation refers to the making of laws and is central for democracies to assure collective selfdetermination. Legislation is also fundamental to preserve liberty as Montesquieu observed for states more than 250 years ago: “In a free state, every man who is considered a free citizen ought to be governed by himself. Hence, the people as a body should have legislative power.” (De l’Esprit des lois, 1748, XI.6, p. 331) In large societies this requires to have representatives who discuss matters of common concern and express the general will. For the European Union, the ordinary legislative procedure is the most important method for producing laws. This article shows that the Treaty of Lisbon introduced a formal conception of legislation. The ordinary legislative procedure is governed by a series of procedural principles which determine the relation between the European Parliament, the Council and the Commission as its main actors. While the Treaties define a formal sequence to adopt legislation, negotiations take place in informal Trilogues between these three institutions. In addition to the procedural principles, the legislative acts adopted must adhere to substantive principles related to their content.