The peritoneum is a serous membrane lining the abdominopelvic cavity. This lining is formed by connective tissue and originates from the mesoderm. The membrane lines both the abdominal walls (as parietal peritoneum) and all of the visceral organs (as visceral peritoneum). The peritoneum supports and suspends the organs within the abdominal cavity and provides an important conduit for the neurovasculature supplying these organs. There are several peritoneal folds, known as mesenteries, omenta, and ligaments. The greater and lesser omenta divide the peritoneal cavity into greater and lesser sacs, which are important anatomic spaces within the cavity. Organs located behind the posterior parietal peritoneum are known as retroperitoneal, while organs that protrude into the cavity and are fully covered by visceral peritoneum are known as intraperitoneal.