Citric acid is a weak organic acid. It is a natural preservative/conservative which occurs naturally in citrus fruits and is also used to add an acidic or sour taste to foods and drinks. In biochemistry, the conjugate base of citric acid, citrate, is important as an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms.

It can exist either in an anhydrous (water-free) form or as a monohydrate.

Citric acid can be used in food coloring to balance the pH level of a normally basic dye.

Also it is an excellent chelating agent, binding metals and is widely used as a pH adjusting agent in creams and gels of all kinds.

Citric acid can be used as a lower-odor stop bath as part of the process for developing photographic film.