In 1956, Werner Heisenberg participated in the second Lindau meeting on physics with a lecture related to his first one, given in 1953. The topic in both lectures is the quantum theory of elementary particles. But the audiences at the two meetings were very different! In 1953, the audience consisted mainly of professional physicists, while the audience in 1956 was dominated by students and young researchers. The change in the audiences reflects the impact of Count Lennart Bernadotte as chairman of the organizing committee. It was his strong belief that most participants should be students and young researchers. This was pointed out in the letters of invitation to the Nobel Laureates, so for his 1956 lecture, Werner Heisenberg was given a task different to the one of 1953. Listening to the lecture, one can hear how Heisenberg solves the problem of addressing both the younger part of the audience and the older physics colleagues in a brilliant way. Very clearly, he first describes the problems that appear when one wants to quantize the relativistic wave equations resulting from a unification of quantum mechanics with the special theory of relativity. Some of the problems of the resulting quantum field theories appear as infinities and Heisenberg tells the story of how these infinities were mastered by the technique of renormalization by the trio of Tomonaga, Schwinger and Feynman, the three recipients of the 1965 Nobel Prize in Physics. After having introduced the scattering matrix and some of its properties, he then turns to his own research group in Göttingen and their attempts to formulate a unified theory of elementary particles. Even though we know today that Heisenberg never reached his goal, it is interesting to listen to his description of the on-going work in this lecture and to compare it with both his 1953 lecture and the two lectures that he gave on the subject later on, in 1959 and 1962.