The Casio F-91W is a digital watch manufactured by Japanese electronics company Casio. Introduced in June 1989[1] as a successor of the F-87W,[2] it is popular for its low price and long battery life.

"Necessity is not the mother of invention, invention is the mother of necessity." These are the words of one of Casio's founders. The people who created Casio were determined to 'invent necessity'- to create products that met latent needs with groundbreaking capabilities no one had ever seen before. Ever since, Casio has been doing just that, bringing new discovery and delight to people around the world. This is Casio's way of building an even more prosperous, richly rewarding world.