Although veterinarians are taught avian anatomy in veterinary school, if one is unfamiliar with its clinical relevance it is always worth refreshing one’s memory. This chapter will highlight those features of avian anatomy and physiology that are relevant to the clinician. It will not seek to be a comprehensive review of the subject. The focus in this chapter is on companion birds and, as such, anatomical structures such as the phallus (found in ratites and waterfowl) will not be discussed. Without a basic understanding of anatomy and physiology, it becomes difficult to understand the pathophysiology of disease and how treatment will affect the patient as a whole.