Proteoglycans are macromolecules formed by a protein backbone to which one or more glycosaminoglycan side chains are co-valently attached. They can be secreted by the cells, retained at the cell surface, or stored in intracellular vacuoles. Hyaluronan is an extremely long glycosaminoglycan which, at variance with other glycosaminoglycans, is released into the extracellular matrix as a free polysaccharide not co-valently linked to a core protein. Both proteoglycans and hyaluronan influence many aspects of cell behaviour by multiple interactions with other molecules. They are involved in matrix formation, cell-cell and cell-matrix adhesion, cell proliferation and migration, and show co-receptor activity for growth factors. Both proteoglycan and hyaluranon synthesis change significantly during ovarian follicle development and atresia. This review describes the structure of these molecules and their possible function in ovarian physiology.