Current commentary in legal and political philosophy conceptualises political parties either as private organisations, immune from legal regulation in their internal affairs, or as quasi-public institutions, where the state may justifiably mandate certain internal regulations. I argue that, in jurisdictions with anti-defection laws, neither conception accounts for the normative status of the political party. Instead, the party ought to be conceptualised as a legislative actor. This paper then examines how conceptualising the party in this way can affect the way in which we understand the relationship between the law and a party. I explore three possible avenues of legal regulation of parties: the process of candidate selection, the selection of party leaders, and interaction between a party and its parliamentary wing. I argue that conceptualising the party as a legislative entity has the most salient implications for the third of these: the interaction between the extra-parliamentary organisation and the parliamentary party.