Hyaluronic acid (HA) is a polysaccharide composed of N-acetylglucosamine and D-glucuronic acid. It is a major component of the extracellular matrix and thus found in many tissues. HA has many effects on the organism (wound healing, cell differentiation, viscoelasticity, embryonic development, anti-aging effect, tissue repair, etc.). The most important factor affecting the biological activity of HA is its molecular weight. Nowadays, it is used in many medical fields such as arthrology, rhinology, oncology, dentistry, ophthalmology, aesthetic medicine, and pneumology including cosmetics. HA can be used with drug molecules in drug delivery systems such as liposomes, micelles, microspheres, and nanoparticles. HA is used in tissue engineering as having the reconstruction and regeneration effect of skin, cartilage, ocular tissues, adipose tissue, and vascular tissues. The moisturizing effect of HA is used in ophthalmology. In addition, HA can be used in the treatment of asthma, chronic sinusitis, chronic obstructive pulmonary disease, and bronchiectasis. With the use of cosmetic products including HA, the moisture retention capacity of the skin increases, its elastic structure is strengthened, and the appearance of wrinkles is removed. Research on the usage areas of HA continues. With these studies, it is aimed to make it more suitable for clinical use.