This text examines the strategies and techniques of Low-External-Input and Sustainable Agriculture (LEISA) in the tropics and analyzes the scientific principles behind them. The central aim of the book is to show development workers how they can assist small-scale farmers in making the best use of low-cost local resources to solve their agricultural problems. Emphasis is therefore on methods of Participatory Technology Development (PTD) to find site-specific solutions and to raise the overall productivity of farming in a sustainable way.