Emotion knowledge in children includes emotion recognition in other peoples' faces, as well as understanding the internal and external causes and consequences of emotions and strategies for regulating them. To date, there is no measure in the German-speaking countries that captures emotion knowledge in a differentiated but also reliable and valid way. The Adaptive Test of Emotion Knowledge (ATEM) aims to close this gap. The ATEM follows an adaptive design and six components of emotion knowledge. The 32 Rasch-scaled items are embedded in an attractive story and vary in their difficulty within and between the components. In a sample of 581 3 - 9-year-olds, the test showed a good fit to a six-dimensional model and very good psychometric properties. In a subsample of 254 3 - 5-year-olds, correlations between the ATEM and a measure of emotion knowledge and measures of expressive and receptive language abilities demonstrated good validity. The ATEM proved to be a good measure of emotion knowledge in children.