About one billion people now live in the slums of the towns and cities of the developing world. And their number is set to double by 2030, unless concerted efforts are made to the contrary. Slums provide an unhealthy and dangerous living environment, and improving the living conditions of slum dwellers is therefore an important international goal. Unfortunately, the official target for doing so falls far short of the numbers affected. Already, the slum residents themselves are the major actors in upgrading their living environment, and there are many good examples of decentralized upgrading. In order to improve the lives of much larger numbers, these examples need to be scaled up. This book examines how this can be done successfully, by investigating a number of case studies and the lessons to be derived from those. It takes as a starting point that the social networks of the urban poor are an important source of information as well as means of communication. But they cannot provide answers to every problem, and one of the key questions is therefore how these networks can be stimulated to link up with other networks or external information sources. The ten case studies cover a range of projects or programmes in different continents, focusing on several issues that affect the lives of slum dwellers, e.g., housing, services, capacity building and income generation. They all have an element of scaling up built into them and the book looks at a range of scaling up methods, including peer training, exchange visits, information networks, and appropriate communication. Thus, the book helps to define what makes good practice up.