This document summarizes concepts and lessons learned from timber legality assurance systems. It discusses the origins of the EU's Forest Law Enforcement, Governance and Trade (FLEGT) Action Plan, which aims to curb illegal logging by strengthening timber legality assurance and licensing for exports. Key elements of legality assurance systems include a legality definition, supply chain controls, verification systems, and independent auditing. Lessons learned include maintaining stakeholder involvement, managing complexity, prioritizing implementation after negotiations, building capacity, and addressing evolving issues over time. FLEGT licensing of legal timber is the goal, but governance reforms along the way also benefit producer countries.