Essilor International S.A. is a French company that produces ophthalmic lenses along with ophthalmic optical equipment. It is based in Paris, France, and quoted on the Euronext Paris Stock Exchange. As one of the 40 largest companies traded in Paris, it is a component of the CAC 40 share index.

Essilor is responsible for creating Varilux, the world's first progressive lens which corrects presbyopia and allows clear vision in the wearer's near, intermediate and far vision. The company formed from the merger of ophthalmic firms Essel and Silor in 1972. Essilor now operates in over 100 countries over five continents. Its activities are largely focused on research and development. It is the world's largest manufacturer of ophthalmic lenses, dominating the market on every continent, and Europe's fourth-largest medical equipment firm.

Essel was founded in 1849 (then-called L’Association Fraternelle des Ouvriers Lunetiers) as a small network of eyeglass assembly workshops in Paris. It quickly expanded in the late 19th and early 20th century through the acquisition of factories in nearby Parisian neighbourhoods and in Eastern France. Essel soon added frame design and trade to its activities. The firm successfully launched an innovative frame design in 1955 called Nylor which is still used today. The Nylor system introduced a thin nylon thread which embraces the lens and is fixed to the frame’s higher branch. Essel's major breakthrough came in 1959 with the revolutionary invention of Varilux, the first ophthalmic progressive lens.