Vascular endothelial cells line blood vessels and play a major role in defining their phenotypic characteristics. Endothelial cells contribute to the servicing of tissues, e.g. by controlling entry of nutrients or immune cells. At the same time they act as custodians of tissue integrity and autonomy. Therefore, not surprisingly, co-ordinated signalling in endothelial cells is critical for tissue health. We primarily study signalling by reversible phosphorylation, mediated by complex networks of protein kinases and phosphatases, in three key areas of endothelial biology.