There are a number of ways in which time affects treaty interpretation. This chapter examines how a text can be understood, in Roland Barthes’s famous expression, as a ‘weapon against time’ (i.e. a device of stability). In international law, such understanding of a text as a safeguard against change is rooted in the principle of contemporaneity, according to which the terms of a treaty shall be interpreted according to the meaning prevailing at the time of its conclusion. Nevertheless, an exception to this principle has emerged in the form of the doctrine of evolutionary interpretation. This chapter thus looks at the ways in which lawyers navigate the tensions between stability and the perceived need for law to respond and adapt to changing social circumstances and present-day conditions. The chapter then turns to the question of subsequent practice and, more precisely, what should be meant by ‘practice’. It also seeks to illuminate the stakes of the debate about the ultimately rejected draft Article 38 of the Vienna Convention, which provided for the possibility of the modification of a treaty by subsequent practice. Finally, the chapter also broaches the question of the boundary between interpretation, law-making, and the emergence of a new rule of customary international law.