The Blow flies RES Handbook is an identification guide to the British species of the three families Calliphoridae, Polleniidae and Rhiniidae, collectively known as the blow flies. Using high quality diagnostic photographs throughout, the Handbook has been created to satisfy the need for an up-to-date identification tool for both enthusiast and professional entomologists. Blow flies are widely distributed and diverse. Many species are seasonal. Biological recorders should be able to find a good list within their local area. But these flies are also of ecological, medical and veterinary interest. As well as pollinating plants and helping to decompose organic matter, they can also spread disease. Egg laying on living animals, particularly livestock, causes myiasis, sometimes leading to death if not treated early enough. In addition, blow flies are an essential tool of forensic entomology. The presence of different species and their stage of development assists in reconstructing the circumstances around suspicious deaths. Hatching time, larval development and pupation are all highly dependent on temperature. The rate of development also varies between species. The author established the Calliphoridae Recording Scheme in 2015. Following taxonomic changes at the family level this has since become the Calliphoridae, Rhiniidae and Polleniidae Recording Scheme. Until recently all three families were part of the Calliphoridae.