Well-known text representation of coordinate reference systems (WKT or WKT-CRS) is a text markup language for representing spatial reference systems and transformations between spatial reference systems.

It exists several coordinate reference systems (CRS) for each body in the solar system. For interoperability issues between the data providers, the IAU identifiers must be defined. Each IAU identifier is related to a CRS, which is defined in the WKT-crs standard. The use of the WKT-crs allows the GIS tools to understand the semantic of the CRS definition. In addition to that, the use of this standard is important so that the IAU identifier can be standardized at OGC later on.