This chapter examines the historical and theoretical foundations of party autonomy. The analysis of the history of party autonomy reveals that it has a distinct background in choice of forum and choice of law, evolving from different sources and justifications. Although arguments related to party autonomy have a long history, these have also long been controversial, and it was only in the twentieth century that party autonomy became widely accepted as a doctrine. There was, however, no single theoretical or doctrinal development which marked the establishment of party autonomy, but rather a gradual evolution. The chapter then examines the theoretical justifications for party autonomy, distinguishing between justifications focusing on the parties and those focusing on public benefits. The former category includes both deontological and consequentialist justifications, while the latter is based solely on a consequentialist approach, often emphasising the role of party autonomy in enhancing regulatory competition. These theoretical justifications largely reinforce each other, but they do suggest different limits to party autonomy. Five particular potential limits are identified, to be explored throughout the book – authenticity, foreseeability, public interests and values, justifiability, and the need for a cross-border element.