recurring behaviour, the belief that the existence of this behaviour is a reason to follow it, and a set of expectations generated by the common knowledge of these circumstances. This characterization is already found in the seminal work of David Lewis, and has been adopted, with some variations, as the starting point of the current discussion on legal conventionalism. The defence of the existence of a connection between legal conventionalism and legal theory has generally been carried out within a positivistic framework. Legal positivists attempt to explain the existence and content of legal systems by making reference to complex social facts. According to them, such facts are dependent on the acceptance of rules, which involve, among other considerations, the adoption of certain conventions on how to recognize or identify those rules. In this respect, the Hartian rule of recognition can be understood as a convention. Taking the previous ideas into consideration, the present work will analyse some of the problems in legal conventionalism, including defining the main features of conventions, the possibility of understanding the rule of recognition as a convention, its role with respect to the existence of legal systems, its normative nature, and the role that conventions play in legal interpretation. All these problems intersect with each other throughout the following chapters. The first part of this book contains the writings of Bruno Celano and Ver?nica Rodr?guez-Blanco, who deal more directly with the problems posed by the notion of convention.