This chapter reviews the basic anatomy and physiology of the anorectum and function of defecation. The anal canal is the terminal portion of the gastrointestinal tract. It is the short tubular segment, distal to the rectum, which is lined internally by squamous and transitional epithelium. The rectum is the distal portion of the large intestine. The neuromuscular anatomy of the anus and rectum is “designed” to preserve fecal continence and to facilitate defecation: withholding stool until it is appropriate to defecate and propelling stool at the time of defecation.