The purpose of this Guide is to demonstrate how to effectively design, test and distribute a retained heat cooker in a field setting. The Guide provides information on the benefits of this improved cooking technology, its typical components, equipment necessary to test its performance, lessons from high performing retained heat cookers, as well as tips on marketing and distributing a retained heat cooker in the field. This Guide serves as an introduction to one type of improved cooking technology that can supplement other cooking practices to reduce indoor air pollution and increase fuel efficiency.