The anal glands or anal sacs are small glands near the anus in many mammals. They are situated in between the external anal sphincter muscle and internal anal sphincter muscle. In non-human mammals, the secretions of the anal glands contain mostly volatile organic compounds with a strong odor, and they are thus functionally involved in communication. Depending upon the species, they may be involved in territory marking, individual identification, and sexual signalling, as well as defense (such as in skunks). Their function in humans is unclear.

Sebaceous glands within the lining secrete a liquid that is used for identification of members within a species. These sacs are found in many species of carnivorans, including wolves, bears, sea otters and kinkajous.

The human anal glands are situated within the wall of the anal canal and communicate with the lumen of the canal via ducts that open at the anal valves, just proximal to the pectinate line. Humans have 12 anal glands on average (which are evenly distributed around the circumference of the anal canal). The glands are situated at varying depths in the wall of the anal canal; some between the layers of the internal and external sphincter (the intersphincteric plane).

In humans, the glands secrete mucin (which differs in composition from that secreted by the rectal mucosa). Their function is unclear.

Anal glands are the most common cause of anal fistula. Large fistulae present a surgical challenge as resection of larger sections of the anal sphincter may result in anal incontinence. The cryptoglandular theory states that obstruction of these ducts^{[clarification needed]}, presumably by accumulation of foreign material (e.g. fecal bacterial plugging) in the crypts, may lead to perianal abscess and fistula formation.

Entry of bacteria into the lumen of the glands can cause infection (which may then spread), and inflammation can prevent drainage of the glands.

Dogs and cats primarily use their anal gland secretions to mark their territory, and generally will secrete small amounts of fluid every time they defecate. Many will often express these glands when anxious or frightened as well. Dogs who are healthy can usually have a wide variety in the appearance of their sac's content. Anal sac fluid varies from yellow to tan or brown in color. The consistency of the fluid ranges from thin, watery secretions to thick, gritty paste. There can also be a range in the malodorousness, or how strongly the contents smell. These factors can all be different from animal to animal.

The inability to effectively express this fluid can lead to anal sacculitis. This is characterized by a build-up of fluid in the anal sac, an uncomfortable condition that can lead to pain and itching. Dogs and cats of any age may be affected, but dogs are far more likely to suffer from anal sacculitis than cats. Dogs and cats with anal glands that do not express naturally may exhibit specific signs, such as scooting the backside upon the ground, straining to defecate, and excessive licking of the anus. Cats may also defecate in areas outside the litter box.