Perchlorates are the salts derived from perchloric acid (HClO₄). Perchlorates are often produced by natural processes but can also be produced artificially. They have been used for more than fifty years to treat thyroid disorders. They are used extensively within the pyrotechnics industry, and ammonium perchlorate is also a component of solid rocket fuel. Lithium perchlorate, which decomposes exothermically to produce oxygen, is used in oxygen "candles" on spacecraft, submarines, and in other situations where a reliable backup oxygen supply is needed. Most perchlorates are soluble in water, except for potassium perchlorate which has the lowest solubility of any alkali metal perchlorate (1.5 g in 100 mL of water at 25 °C).

The chemical notation for the perchlorate ion is ClO−
4. The ion has a molecular mass of 99.45 amu.

A perchlorate (compound) is a compound containing this group, with chlorine in oxidation state +7.

The perchlorate ion is the least reactive oxidizer of the generalized chlorates. This appears to be a paradox, since higher oxidation numbers are expected to be progressively stronger oxidizers, and less stable. A table of reduction potentials of the four chlorates shows that, contrary to expectation, perchlorate is the weakest oxidant among the four in water.