This chapter explores two essential legal systems, the civil law system and the common law system, as a foundation to trace the origins and features of legal English. The main aim of this chapter is to present a chronological account of the evolution of legal English in order to show how the unique features of modern legal English arise from sociolinguistic interactions over various historical periods. Current views on legal English are influenced not only by historical elements specific to this linguistic form but also by the lasting impact of historical strata. These serve as markers of linguistic conservatism, thus revealing a greater stability in legal terminology compared to the wider linguistic landscape. Furthermore, this chapter will discuss the rise of the plain language movement, which emerged as a reaction to the complexity and inaccessibility of conventional legal language. By examining both historical progressions and modern initiatives aimed at enhancing clarity, this chapter seeks to offer an understanding of how legal language has transformed and continues to evolve in response to societal demands.