When flies are used for therapeutic purposes to treat wounds (maggot therapy), they may be referred to as medicinal flies. Species that have been used for maggot therapy or which are likely candidates for maggot therapy generally belong to the family Calliphoridae, commonly known as blowflies. These flies have ecological relationships, life-history patterns, physiologies, and nutritional requirements that help them exploit cadavers as well as living bodies. The same adaptations can also be harnessed to treat non-healing necrotic wounds. This chapter first introduces the general features of dipteran diversity, morphology, and biology before a closer examination of the family Calliphoridae.