Cornstarch is the starch of the maize grain, commonly known as corn. It has a distinctive appearance and feel when mixed raw with water or milk, giving easily to gentle pressure but resisting sudden pressure. It is usually included as an anti-caking agent in powdered sugar (10X or confectioner's sugar). For this reason, recipes calling for powdered sugar often call for at least light cooking to remove the raw cornstarch taste.

Cornstarch is often used as a binder in puddings and similar foods. Most of the packaged pudding mixes available in grocery stores include cornstarch. Cornstarch puddings may be easily made at home, benefitting from the use of a double boiler. The most basic such pudding may be made only from milk, sugar, cornstarch and a flavoring agent.

It is also used as a thickener in many Chinese recipes and French sauces, although in the latter case it is generally used as a time-saver to replace more traditional, time-consuming methods.

Cornstarch also has many uses in the manufacturing of environment-friendly products. For example, in 2004, the Japanese company Pioneer announced a bio-degradable Blu-Ray disc made out of cornstarch.

A mixture of equal volumes cornstarch and water (sometimes called oobleck) is a popular classroom demonstration of a dilatant (shear-thickening) fluid. When struck, cut with a knife, or worked vigorously in the hands, it behaves like a pliable solid, but if allowed to sit for a few seconds, it flows as a viscous liquid.