Peritoneal carcinomatosis and malignant ascites are not independent disease entities but manifestations of various heterogeneous malignancies. The quality of life of affected patients is typically severely compromised due to pain, gastrointestinal dysmotility and large quantities of ascites, and the prognosis is usually poor. Recent improvements in symptom control and also prognosis have placed increased emphasis on the complex of peritoneal carcinomatosis and malignant ascites. In particular, trifunctional antibodies prove to be a novel therapeutic option. This book discusses common features in pathogenesis, diagnostic investigation and treatment as well as differentiated treatment approaches according to underlying diseases.