Gastro-intestinal (GI) disease is a very common problem in small animal practice and its diagnosis depends on both the subjective interpretation of gross endoscopic images and histopathological assessment of endoscopic biopsy specimens. An increasing number of veterinarians are performing endoscopic biopsy of the GI tract as the availability of the equipment improves and its price declines. However, there is a significant lack of experience and expertise in endoscopic diagnosis within the veterinary profession, and limited agreement about histopathological interpretation. This atlas aims to inform both endoscopists and histopathologists what they are looking at. This book is a pictorial atlas and not a standard textbook, and uses the highest quality video-endoscopic images to illustrate lesions. The images of related histopathology strengthen this book as they will be the preferred publication vehicle of the World Small Animal Veterinary Association (WSAVA) GI Standardization Group, which has been empowered to lay down standards in small animal gastroenterology. Additional illustrations of cytology, radiography and ultrasound related to specific conditions further increase the interest and value for the reader. The proposed book has minimal text and is composed largely of high quality images of normal and diseased GI tract in dogs and cats. This atlas acts as a visual guide to both endoscopic practitioners and histopathologists in both academia and private practice. All the members of the WSAVA GI Standardization Group are recognised specialists in small animal gastroenterology and all contribute. This atlas is the gold standard by which all endoscopic diagnoses are made.