Endothelial cells (EC) are currently used as in vitro model systems for various physiological and pathological processes, especially in angiogenesis research. Primary EC have a limited lifespan and display characteristics that differ from batch to batch due to their multidonor origin. In recent years many groups have established EC lines. This Review gives an overview of the advantages and disadvantages of currently available vascular EC lines. Its aim is to help the investigator to decide which cell line matches his or her research goal best. Truly immortalized cell lines are generally better characterized and more stable in their endothelial traits than EC that were given an extended life span. Presently the best characterized macro- and micro-vascular EC lines are EA.hy926 and HMEC-1, respectively.