Monofluorophosphate is an anion with the formula PO₃F²⁻, which is a phosphate group with one oxygen atom substituted with a fluoride atom. The charge of the ion is −2. The ion resembles sulfate in size, shape and charge, and can thus form compounds with the same structure as sulfates. These include Tutton's salts and langbeinites. The most well-known compound of monofluorophosphate is sodium monofluorophosphate, commonly used in toothpaste.

Related ions include difluorophosphate (PO
2F−
2) and hexafluorophosphate (PF−
6). The related neutral molecule is phosphenic fluoride PO₂F.

Organic derivatives can be highly toxic and include diisopropyl fluorophosphate.

Willy Lange from Berlin discovered sodium monofluorophosphate in 1929. He fruitlessly tried to make monofluorophosphoric acid. However, he did discover the highly toxic organic esters. Following this discovery various nerve gases like sarin were developed.

Fluorophosphate glasses are low melting point kinds of glass which are mixtures of fluoride and phosphate metal compounds. For example, the composition 10% SnO, 40% SnF₂, 50% P₂O₅ forms a glass melting about 139 °C. PbO and PbF₂ can lower the melting temperature, and increase water resistance. These glasses can also be coloured by various other elements, and organic dyes.

Hydrolysis of difluorophosphate with an alkali produces monofluorophosphate.

Industrial production is by reaction of a fluoride with a metaphosphate.

Disodium hydrogen phosphate or tetrasodium pyrophosphate can react with hydrogen fluoride to form the sodium salt.

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