The peritoneum is an extensive serous organ with both epithelial and mesenchymal features and a variety of functions. Diseases such as inflammatory peritonitis and peritoneal carcinomatosis can induce disturbance of the complex physiological functions. To understand the peritoneal response in disease, normal embryonic development, anatomy in healthy conditions and physiology of the peritoneum have to be understood. This review aims to summarize and discuss the literature on these basic peritoneal characteristics. The peritoneum is a dynamic organ capable of adapting its structure and functions to various physiological and pathological conditions. It is a key element in regulation of inflammatory responses, exchange of peritoneal fluid and prevention of fibrosis in the abdominal cavity. Disturbance of these mechanisms may lead to serious conditions such as the production of large amounts of ascites, the generation of fibrotic adhesions, inflammatory peritonitis and peritoneal carcinomatosis. The difficulty to treat diseases, such as inflammatory peritonitis and peritoneal carcinomatosis, stresses the necessity for new therapeutic strategies. This review provides a detailed background on the peritoneal anatomy, microenvironment and immunologic responses which is essential to generate new hypotheses for future research.