This chapter examines the relationship between peace treaties and territorial change. Distinguishing peace treaties from other related agreements, it analyses the critical role that peace treaties play in the acquisition of territorial sovereignty following the use of force, both under contemporary and classical international law. In this regard, it maintains that, besides cases of debellatio, conquest alone was never a valid title to territorial sovereignty. Based on the difference of the applicable legal regimes, it distinguishes peace treaties concluded between independent states from those concluded as part of the process of accession of a people to independence, as well as from those concluded with successful secessionist entities. In addition, particular attention is paid to the great variety of territorial clauses contained in peace treaties.