A growing awareness of the devastating impact of weapons of mass destruction (WMD) on international peace and security inspired multilateral efforts in the 20th century to alleviate the threat posed by these weapons. These efforts culminated in the adoption the Nuclear Non-proliferation Treaty (1968), the Biological and Toxin Weapons Convention (1972) and the Chemical Weapons Convention (1997). This complex of WMD disarmament regimes, which was expanded by the recent adoption of the Treaty on the Prohibition of Nuclear Weapons in 2017, provides legal frameworks for reducing, and eventually eliminating, all WMD stockpiles. The disarmament literature tends to place a focus on political, technical, scientific and military aspects surrounding the implementation of disarmament regimes, while largely neglecting their legal architecture and the wider role of international law in the field of disarmament. However, developments in recent years, including the ad hoc chemical disarmament of Syria, the Marshall Islands lawsuit brought against the nuclear weapons states at the International Court of Justice (ICJ), and the adoption of the new treaty on nuclear weapons, have accorded increased attention to international legal aspects surrounding disarmament. In the context of these movements, this thesis intends to make a two-fold contribution. First, it addresses gaps in the disarmament literature by offering a comprehensive up-to-date analysis of the international law on disarmament, including of recent legal debates. As a second contribution, it will provide a novel evaluation of the legal effectiveness of disarmament regimes by identifying criteria which are considered crucial for successful disarmament and applying them to the respective WMD regimes. Through this dual examination of legal and practical aspects surrounding disarmament, this thesis aims to offer useful insights and support to both international legal scholars and disarmament practitioners in the appropriate interpretation, implementation and strengthening of disarmament regimes.