The Cajal course is an intensive three-week course that guides participants through the theory and practice of state-of-the-art methods for addressing pertinent questions in this field of research. This course will teach the latest technological advances in optical, electrophysiological, genetic, viral tracing, anatomical, and optogenetic approaches for the study of neural circuits. Students will learn the current state of knowledge of how neural circuits are organized, especially in the mammalian mouse brain, and how information can be processed in biological circuits through population-based activity patterns. The faculty will consist of international experts in their respective fields, discussing fundamental concepts and their own research, introducing methods relevant for neural circuit research, and providing hands-on projects. Students will perform experimental projects to apply these methods to scientific problems, they will learn how to analyse acquired data, and they will discuss strengths and limitations of the various techniques.