The Madrid International Plan of Action on Ageing is the most important United Nations (UN) document on population ageing for 20 years and sets the context for global policies on ageing for the current century. Drawing from the authors' active participation in the preparation of the draft that formed the basis of the Madrid Plan, the primary purpose of this article is to describe the two-year process of development of the Plan. Then the main features of the Plan are outlined, including the pivotal role of the society for all ages concept and its thematic foundations. The Madrid Plan is contrasted with its Vienna predecessor of 20 years earlier – the priority given to developing countries in the former is identified as one of the key differences between them. Following a brief outline of the implementation and monitoring processes for the Madrid Plan, a model is presented as a potential template for use in evaluating the impact of the Plan and, especially, its effectiveness in improving the conditions of older people's lives. It is argued that a systematic process of monitoring and evaluation is required if the Plan is not to suffer the fate of being regarded as yet another worthy ‘wish list’.