Inflammatory disorders of the peritoneum and mesentery represent a diverse group of diseases with a variety of different etiologies. Many of these disorders can be classified as distinct manifestations of multisystem rheumatologic or vasculitic disease, arising in the context of a broader syndrome. At the same time, inflammatory diseases can also emerge intrinsically as primary peritoneal disorders, which can have a far-reaching impact on other organ systems in the intraabdominal space. In both cases, diseases with predominantly peritoneal or mesenteric pathophysiology are rare, and the majority of these diseases are still poorly understood. This chapter aims to not only provide a foundation for understanding inflammatory disorders of the peritoneum and mesentery but to also shed light on future areas of research for these unique conditions.