Sodium silicate is a generic name for chemical compounds with the formula Na
_2xSi
_yO
_2y+x or (Na
₂O)
_x·(SiO
₂)
_y, such as sodium metasilicate Na
₂SiO
₃, sodium orthosilicate Na
₄SiO
₄, and sodium pyrosilicate Na
₆Si
₂O
₇. The anions are often polymeric. These compounds are generally colorless transparent solids or white powders, and soluble in water in various amounts.

Sodium silicate is also the technical and common name for a mixture of such compounds, chiefly the metasilicate, also called waterglass, water glass, or liquid glass. The product has a wide variety of uses, including the formulation of cements, passive fire protection, textile and lumber processing, manufacture of refractory ceramics, as adhesives, and in the production of silica gel. The commercial product, available in water solution or in solid form, is often greenish or blue owing to the presence of iron-containing impurities.

In industry, the various grades of sodium silicate are characterized by their SiO₂:Na₂O weight ratio (which can be converted to molar ratio by multiplication with 1.032). The ratio can vary between 1:2 and 3.75:1. Grades with ratio below 2.85:1 are termed alkaline. Those with a higher SiO₂:Na₂O ratio are described as neutral.