This chapter reviews and analyzes the effects of crowding on lipid membranes. Presented data shows that due to steric effects crowding on one side of the bilayer causes membrane bending toward that side. The curvature of the membrane increases with increasing crowding, with disordered proteins being more effective in generating deformations. The effect of crowding on lateral diffusion in the vicinity of the membrane is discussed, highlighting the difference between crowding and immobilization by fixed scaffolds. The effect of membrane crowding by integral proteins is also analyzed and it is shown that it leads to lipid deformations near proteins, promotes the formation of lipid microdomains and protein clusters. The role of the crowding agent effects on the physicochemical properties of solutions is reviewed and the evidences are given for the different effects of uniformly distributed macromolecules and of proteins within the membrane-associated condensate, formed by liquid phase separation. In summary, the review and analyzes show that the role of various crowding effects on membranes has been significantly underestimated and a reliable understanding of biological membranes cannot be built without considering the effects of crowding.