Sulfate is the IUPAC name for the SO₄^2- ion, consisting of a central sulfur atom single bonded to four tetrahedrally oriented oxygen atoms. This anion has a net negative two electric charge.

Almost all ionic compounds with sulfate anions are soluble in water at standard temperature and pressure (the exceptions include CaSO₄, SrSO₄, and BaSO₄).

The acid of the sulfate ion is H₂SO₄, called sulfuric acid.

Sulfates, also known as sulfur oxides, are important in both the chemical industry and biological systems:

• The Lead-acid battery typically uses sulfuric acid.
• Organisms living near deep sea thermal vents depend on sulfates for energy in lieu of the sun.
• Copper sulfate is a common algaecide.
• Magnesium sulfate, commonly known as Epsom salts, is used in therapeutic baths.

Sulfates occur as microscopic particles (aerosols) resulting from fossil fuel and biomass combustion. They increase the acidity of the atmosphere and form acid rain. There is a negative radiative forcing from aerosols because, while in the atmosphere, they reflect incoming solar radiation. This is an increase in albedo.