Endothelial cells perform a number of important functions in the organism, and their dysfunction plays an important role in pathogenesis of a wide range of diseases. This review deals with the current literature data on structural characteristics of endothelial cells. A special section is devoted to endothelial cells development and differentiation. Structural aspects of endothelial cells cytoplasm and transport structures organization are discussed. Particular attention is paid to the structural heterogeneity of endothelial cells. Data on planar and apical- basal polarity of endothelial cells are reviewed separately.