The major proteoglycan of articular cartilage is a protein-polysaccharide of great complexity. The structure of this macromolecule is described in this article and is correlated to the function of proteoglycans within the extracellular matrix of cartilage. Chondrocytes, which comprise the cell population of cartilage, are responsible for the synthesis of proteoglycans. A description of the synthesis of proteoglycans reflects the complex nature of these macromolecules and involves a number of sites within various organelles of the chondrocyte. The pathway of proteoglycan synthesis is discussed in addition to the intracellular and extracellular events involved in the regulation of their biosynthesis.