This book provides a systematic introduction of composting principles and procedures. Its focus is on the methodology of co-composting of organic solid waste and dewatered sewage sludge using the windrow (pile) method. Thus, this book presents "state-of-the art" knowledge and provides information necessary for both undergraduate and graduate studies on organic waste management. The target groups for the book are professionals, consultants, academics, and BSc and MSc students whose backgrounds may be engineering or natural sciences.Globally, there is increasing focus on reducing pollution from the organic fraction of municipal solid waste. Therefore, there will be the need for experts in environmental technologies and management of organic solid waste. The essence of this book is to introduce the consultants, engineers and academics to the biotechnological process of managing organic solid wastes. A brief introduction is given for why the need for environmentally friendly process of managing organic solid waste. Finally, and most importantly, the book describes an appropriate ratio of the substrates that can ensure good quality compost.