This text provides an overview of the applications of diagnostic ultrasonography in the horse. It discusses the normal anatomical relationships from an ultrasonographic perspective, the techniques utilized to obtain ultrasonographic images, and the lesions or injuries which can be imaged through ultrasound. The use of ultrasonographic information to develop a prognosis and follow the progress of the case is also addressed. Contents: Physics and Instrumentation. Artifacts and Variants. Musculoskeletal Ultrasonography. Thoracic Ultrasonography. Cardiovascular Ultrasonography. Abdominal Ultrasonographyin the Adult Horse. Pediatric Abdominal Ultrasonography. Ultrasonography of the Genital Tract of the Mare. Fetal Ultrasonography. Ultrasonography of the Genital Tract of the Stallion. Ultrasonographic Evaluation of Small Parts.