The present thesis explores the notion of legal capacity and supported decision-making as enshrined in Article 12 of the United Nations Convention on the Rights of Persons with Disabilities. The thesis begins by outlining the policy context, how guardianship has been progressively criticised and reformed and how the notion of supported decision-making gradually expanded until the genesis of Article 12. A narrative review explores how scholars have grappled with the meaning of supported decision-making and attempted to define what it means concretely. Many questions remain largely unanswered and there is a need for guidance on how Article 12 can be implemented in practice, how to operationalise Article 12 and make sure that supported decision-making is also available to people with high support needs. This review is followed by an analysis of four pilot studies that were previously evaluated and findings made publicly available. It concludes that the existing evaluations do not provide answers in sufficient detail to allow the construction of a tool to analyse the implementation of Article 12 in practice. The second part of this thesis thus responds to the gaps identified in the previous literature and evaluations. To do so it explores the aims, methodology, outcomes and lessons learnt in six pilot projects seeking to implement supported decision-making in different parts of the world. An analytical framework, based on the findings of previously reviewed literature and theory, delineates nine domains that serve to analyse the impact and outcomes of each pilot project. Detailed analysis of the six pilot projects concludes that, although the pilot projects go some way towards operationalising and implementing Article 12, there remain many gaps in this respect. This thesis concludes with the discussion of the findings and the consideration of implications for research, policy development and new pilot projects to achieve a real culture change. Several structural barriers and challenges need to be solved to advance Article 12 implementation. Resistance to changes, gaps in policy and practice, lack of infrastructure remain the principal challenges ahead. Successful implementation of Article 12 implies to encourage a culture of change, working on law, policy, practice and training programmes in synergies.