Blood and other body f luids contain cell-derived microvesicles. The presence of microvesicles in cancer patients was already noticed in the late 1970s. Since then, the prothrombotic state in cancer patients has invariably been associated with the presence of such microvesicles. More recently, a growing body of evidence supports an important contribution of microvesicles to cancer cell survival, invasiveness and metastases. Here, we will present an overview of the many contributions of microvesicles to cancer development and progression. In addition, their role in risk stratification and treatment of cancer patients is discussed.