Clouds are fascinating and feature a great variety ranging from small cumulus clouds or large strato-cumulus decks up to tall thunderstorms. At the same time, clouds are among the largest sources of uncertainty in weather and climate forecast. Why? Clouds aren’t isolated objects; they influence nearly all atmospheric quantities (wind, solar radiation, humidity, etc.) and interact with the ambient air in a complex manner. That is the reason why clouds are one of the biggest, yet not fully understood mysteries in weather and climate research. The Meteorological Institute in cooperation with other research institutions like e.g. the Max-Planck Institute for Meteorology uses satellite observations; ground based remote sensing, aircraft measurements and numerous numerical models to lift the secrets of clouds. However, they will always be an extremely beautiful and high-flying research topic!