The cellular and molecular biology of mesothelioma is a complicated, multifactorial, incompletely understood process of carcinogenesis. Normal mesothelial cells can be transformed into a malignant phenotype by multiple factors, usually asbestos. Several tumor suppressor genes may be lost, and several oncogenes can be activated. A local environment of inflammation with associated release of cytokines may promote deregulated cell growth. The release of immunosuppressive substances such as nitric oxide may contribute to this process. The interaction of asbestos and viral DNA incorporation is unclear but warrants further investigation. In the majority of mesothelioma patients, present standard therapies have little effect on survival. Clinical trials studying a variety of innovative treatment strategies are being performed at centers with a significant referral base for the disease. Future treatments, however, must be based on understanding of the biology of mesothelioma.