This book looks at regulation, policy and implementation of framework agreements, supplier lists and other similar public procurement tools, with a strategic and pragmatic perspective. Whilst procurements of huge volumes and value are performed worldwide through such tools on a daily basis, and despite their complexity and diversity, this topic has rarely been studied in a systematic way. The book fills this major gap. It examines a series of public procurement systems or legal instruments selected to ensure wide coverage - the UNCITRAL Model Law on Public Procurement, the World Bank, the US federal procurement system, EU law, France, Romania, and the UK pre- and post-Brexit. By deconstructing over 20 'clusters' of tools into their key features along a pattern for analysis, the book reconstructs a conceptual framework for purchasing uncertain or indefinite requirements through a transversal perspective across public procurement systems. In this way, the book provides valuable orientation to law and policy makers for improving or reforming this area, to procurement officers in interpreting existing regulation and identifying innovative practical solutions, and to lawyers and the judiciary for a balanced application of the regulation. The book delivers essential material for procurement of uncertain or indefinite requirements.