Kaposi sarcoma (KS) is an unusual vascular tumour caused by an oncogenic-herpesvirus, Kaposi sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8 (HHV 8). KS lesions are characterized by an abundant inflammatory infiltrate, the presence of KSHV-infected endothelial cells that show signs of aberrant differentiation, as well as faulty angiogenesis/ vascularization. Here we discuss the molecular mechanisms that lead to the development of these histological features of KS, with an emphasis on the viral proteins that are responsible for their development.