Hyaluronic acid (HA) is a natural polysaccharide primarily present in the vitreous humor and in cartilages where it plays a key structural role in organizing the cartilage extracellular matrix. HA is used in a wide range of applications including treatment of arthritis (as a viscosupplementation agent for joints) and in a variety of cosmetic injectable products. Its safety profile is thus well established. Thanks to its high biocompatibility and targeting properties, HA has also been investigated for use as a carrier of anticancer drugs and, recently, also of proteins. Its role in the last case is a particularly challenging one as dedicated coupling chemistries are required to preserve the protein's conformation and activity. This study focuses on the state of the art on protein HAylation. New data from our laboratory on the local delivery of specific biologics to joints will also be outlined.