The abdominal cavity is lined by the peritoneum, a membrane that covers not only the inside wall of the cavity (parietal peritoneum) but also every organ or structure contained in it (visceral peritoneum). The space between the visceral and parietal peritoneum, the peritoneal cavity, normally contains a small amount of serous fluid that permits free movement of the viscera, particularly of the gastrointestinal tract, inside the peritoneal cavity. The peritoneum, by connecting the visceral with the parietal portions, assists in the support and fixation of the abdominal organs. The diverse attachments of the peritoneum divide the abdominal cavity into several compartments.

Some of the viscera are attached to the abdominal walls by broad areas of the peritoneum, as is the pancreas. Others, such as the liver, are attached by folds of the peritoneum and ligaments (ligament), usually poorly supplied by blood vessels.

The peritoneal ligaments are actually rather strong peritoneal folds, usually connecting viscera to viscera or viscera to the abdominal wall; their name usually derives from the structures connected by them (e.g., the gastrocolic ligament, connecting the stomach and the colon; the splenocolic ligament, connecting the spleen and the colon) or from their shape (e.g., round ligament, triangular ligament).

The mesenteries (mesentery) are folds of peritoneum that are attached to the wall of the abdomen and enclosing viscera. They are richly supplied with vessels that carry blood to or from the organs they enfold. The three most important mesenteries are the mesentery for the small intestines; the transverse mesocolon, which attaches the transverse portion of the colon to the back wall of the abdomen; and the mesosigmoid, which enfolds the sigmoid portion of the colon.

The omenta are folds of peritoneum enclosing nerves, blood vessels, lymph channels, and fatty and connective tissue. There are two omenta: the greater omentum hangs down from the transverse colon of the large intestine like an apron; the lesser omentum is much smaller and extends between the stomach and the liver.

Common afflictions of the abdominal cavity include the presence of fluid in the peritoneal cavity ( ascites) and peritonitis, an inflammation of the peritoneum.