Castor oil is generally a non-edible vegetable oil obtained by pressing the seeds of the castor oil plant (Ricinus communis). It is a triglyceride in which approximately 90 percent of fatty acid chains are ricinoleate. Oleate and linoleates are the other significant components.
Castor oil and its derivatives are used in the manufacturing of soaps, lubricants, hydraulic and brake fluids, paints, dyes, coatings, inks, cold-resistant plastics, waxes and polishes, nylon, pharmaceuticals, and perfumes.
Castor oil is famous as a source of ricinoleic acid, a monounsaturated, 18-carbon fatty acid. Among fatty acids, ricinoleic acid is unusual in that it has a hydroxyl functional group on the 12th carbon.

In the food industry, castor oil (food grade) is used in food additives, flavorings, candy (e.g., polyglycerolpolyricinoleate or PGPR in chocolate), as a mold inhibitor, and in packaging. Polyoxyethylated castor oil is also used in the food industries.

In India, Pakistan, Nepal, and Bangladesh, food grains are preserved by applying castor oil. It stops rice, wheat, and pulses from rotting. For example, the legume toor dal is commonly available coated in oil for extended storage.

The United States Food and Drug Administration (FDA) has categorized castor oil as "generally recognized as safe and effective" (GRASE) for over-the-counter use as a laxative with its major site of action the small intestine where it is digested into ricinoleic acid.