Commissioned by the United Nations Secretary General in 2000, and completed in 2005, the Millennium Ecosystem Assessment (MA), based on the findings of 34 'sub-global' assessments carried out in a diverse set of ecosystems in sites around the world, provides a state-of-the-art appraisal of the condition and trends in the world's ecosystems and the services they provide. The MA presents compelling evidence that underlines the urgency and necessity of restoring, conserving, and sustainably managing our ecosystems. Most important, the assessment shows that, with appropriate actions, it is possible to reverse the degradation of many ecosystem services over the next 50 years. By providing invaluable information to policy makers, the MA seeks to help ensure that the required changes in current policy and practice undertaken will be evidence based and informed by the best available scientific analysis. This manual, Ecosystems and Human Well-being: A Manual for Assessment Practitioners, allows for the wider adoption of the MA conceptual framework and methods. The manual, which contains numerous case studies of best practice, offers a practical guide for undertaking ecosystem assessments and includes tools and approaches that can assess options for better managing ecosystems. This Manual makes the methods of the MA and associated sub-global (local and regional) assessments widely accessible. While the MA is the most comprehensive assessment of ecosystems carried out to date, there are other related assessment processes such as Global Environment Outlook (GEO), Global International Waters Assessment (GIWA), Intergovernmental Panel on Climate Change (IPCC), Land Degradation Assessment in Drylands (LADA), International Assessment of Agricultural Knowledge, Science and Technology for Development (IAASTD) and World Water Assessment. Lessons learned from these assessments supplement the best practice of ecosystem assessment identified through the MA. The publication of this Manual aims to encourage more assessments at scales which are relevant to policy and decision makers.