This Atlas describes the classification system for clouds and meteorological phenomena used by all WMO Members. The classifications also describe meteorological meteors other than clouds – hydrometeors, lithometeors, photometeors, and electrometeors. The Atlas provides a common language to communicate cloud observations, and ensures consistency in reporting by observers around the world. It serves as a training tool for meteorologists, as well as for those working in aeronautical and maritime environments, and it has become popular with weather enthusiasts and cloud spotters.

The text enclosed in grey-shaded boxes comprises Annex I to the Technical Regulations (WMO-No. 49) and has the legal status of standard practices and procedures.