This paper traces the evolution of Palestinian Arab proto-self-determination and “peoplehood” during the Mandate for Palestine. In doing so, it seeks to clarify what are two of the most controversial and emotive concepts in international legal discourse and popular imagination today, “Palestine” and “Palestinian,” concepts that were understood quite differently during the time of the Mandate between the First and Second World Wars and until the 1948 War than they are understood today. This paper begins by describing the Mandate system and the territorial dispensation for Palestine that was secured within it. Taking the view that the Mandate system sought to secure some permutation of what one might understand as a type of proto-self-determination, it then assesses the extent to which one can reasonably conclude that a specifically Palestinian Arab “people” existed at the time in a juridical sense. This paper’s final substantive section draws upon evidence that States gave to the United Nations Special Committee on Palestine in 1947 and the United Nations’ work on the question of Palestine up to the 1948 War. This paper shows that rediscovering the evolution of Palestinian Arab proto-self-determination and “peoplehood” during the Palestine Mandate reveals the malleability of these concepts, something that remains the case, at least to a certain extent, to the present.