Students will gain deep insights into the concepts and practice of physical organic chemistry. In contrast to previous lectures in organic chemistry, physical organic chemistry is concerned with fundamental aspects of (organic) structure and reactivity and with the question ”how do/did we find out about this?” So, this lecture is not about learning reaction mechanisms (by heart), but the focus lies on concepts, metrics, methods and techniques. The thermodynamics and kinetics of organic reactions represent the core of this lecture, but newer aspects such as systems chemistry and catalysis will be covered as well.