As part of the Science and Art Festival, the meeting on “The whole and the sum – The complexity between physics, music and urban spaces” was held in Rome on 19 June. Moderated by Felice Cimatti, physics Francesca Tria, the architect Lorenzo Romito and the composer Stefano Mainetti spoke on the topic. Everything around us is a complex system, including ourselves. Complex is the brain, the organism, the interactions between us and with all other life forms on Earth. The parts that make up these systems are not simply close to each other but, by interacting, they become capable of developing what we call collective behaviors. This is how complex systems exhibit one of their most astounding characteristics: the whole becomes richer than the sum of the parts, each in a particular sense. As Giorgio Parisi writes “All simple systems are equally simple; every complex system is complex in its own way”.