This collection is dedicated to articles presenting so called CAMELS (Catchment Attributes and Meteorology for Large-sample Studies) data. CAMELS hydro-meteorological datasets are nationwide compilations of hundreds of identified catchments, their physical attributes, records of their drainage dynamics and corresponding meteorological time series. CAMELS data have revolutionised the way hydrological predictions, catchment classifications, and analyses of characteristics and change are carried out. They have unified approaches to the identification of hydrological signatures, serve as benchmarks for model development in a variety of settings, and give rise to a new branch of machine learning in water management. CAMELS data are a testimony to international open data initiatives and demonstrate how regional to global science, education and management practice benefit from open data.