Ralston Purina was a major American corporation best known for its production and marketing of animal feeds.

Purina was based in St. Louis, Missouri. It was famed for its "checkerboard" pattern that it used on its product packaging, which was an important trademark, and hence its headquarters was called Checkerboard Square. At one point it owned an interest in the St. Louis Blues National Hockey League team; during this period the arena they then used was referred to as the "Checkerdome". The Purina name was principally associated with the animal feed business, which included feed for livestock and household pets. The predominant brand for each animal was generally referred to as "Chow"; hence there was "Purina Horse Chow", "Purina Dog Chow", "Purina Cat Chow", and even "Purina Monkey Chow". The "Ralston" name was more associated with food for humans; soda crackers and a farina cereal, among other products, were marketed under this name. Ralston Purina also for many years produced the familiar line of "Chex" cold breakfast cereals. The two businesses were seemingly only tenuously related; eventually the food division was sold off, and today "Chex" are made by General Mills.

The animal feed business became the subject of a takeover bid by Swiss-based Nestlé, whose "Friskies" brand was the other leading brand of pet food in the U.S. This bid was eventually accepted in 2001. Several brands of pet food (e.g., "Meow Mix") had to be divested separately to meet antitrust concerns. Purina brands are now made and marketed by a division of Nestlé.