This Médecins Sans Frontiers (MSF) paper looks at how patents adversely affect access to affordable medicines. Although effective medicine is available to treat many global diseases, one-third of the world's population lacks access to these basic, but expensive, drugs as a result of patent rights. While the Trade Related Aspects of Intellectual Property Rights (TRIPS) Agreement of the World Trade Organisation (WTO) is meant to ensure that patent protection does not limit access to medicines, the ability of national governments to implement TRIPS in a way that ensures access to medicine is highly problematic.