Caveolae are small, bulb-shaped plasma membrane invaginations that account for up to half the membrane surface area of endothelial cells. Mutations that ablate caveolae lead to diverse phenotypes in mice and humans, making it challenging to uncover their molecular mechanisms. Caveolae have been described to function in endocytosis and transcytosis (a specialized form of endocytosis) and in maintaining membrane lipid composition, as well as acting as signaling platforms. New data also support a model in which the central function of caveolae could be related to the protection of cells from mechanical stress within the plasma membrane. I will present in vitro and in vivo experiments confirming a mechanoprotective role, and present recent data on the molecular architecture and function of caveolae.