This book deals with the treatment and valorization of some by-products of the agro-food industries. Some ways of recovery of by-products have been mentioned in this book such as composting, methanization, extraction of bioactive molecules, energy recovery and recovery in animal feed. The choice was made on the by-products of six agri-food industries namely: The olive industry, meat industries and fishery products, the dairy industry and that of fruit juices and distillery. Some value chains and applications of products derived from by-products have been presented in this book.