This chapter addresses the interaction between the general regime of State succession to treaties, and recent investment law practice relating to it. It begins by highlighting a particular feature of this interaction: unlike other general regimes of public international law, the general regime of State succession has not been codified in a widely accepted text, and aspects of it remain contested. Against this background of partial normative uncertainty, the chapter assesses investment treaty practice and arbitral awards. It shows that these have had three distinct impacts: First, as far as succession to membership in treaties establishing international organisations is concerned, investment law practice affirms the orthodox approach, which at times was said to come under pressure: new States do not automatically succeed to membership positions of their predecessor States. Second, as regards the central question of whether new States succeed to BITs agreed by their predecessors, investment practice points towards a nuanced approach: tribunals seem reluctant to accept a rule of automatic succession, but have seriously engaged with the possibility of implied succession based on conduct. Third, in cases of cessions of territory, investment decisions emphasise the ‘moving treaty frontier principle’, and construes exceptions to it narrowly: treaties of the successor, as a default rule, become applicable to the ceded territory. Overall, the chapter argues that investment practice works from within the general regime, but consolidates and moulds it, at times confirming trends, adding texture, specificity and nuance.