This chapter examines the notion of consent to be bound from the point of view of its motion and change from a classical concept included in the Vienna Convention on The Law of Treaties (VCLT), to its evolution in modern times. It also analyses the question of reservations to treaties, which was one of the projects of the International Law Commission. The chapter deals with the contentious issue of reservations to human rights treaties. The chapter also demonstrates that since consent to be bound is integral to the whole system of treaty law, it can also be identified in situations where we have an increase (auxesis), diminution (meiosis) or even alteration (alloiosis) of the treaty, as can happen when we are dealing with the system of reservations.