A collection of essays on the significance of science in the modern world. There are minor shortcomings: the essays are uneven and some of their content is repetitive. But these pitfalls are overshadowed by the profound unity of thought, the ease with which Heisenherg shuttles between different realms of knowledge, and his elegance of style. His interlocutors are Einstein and Planck but also Goethe and Plato. These are some of the central themes: modern physics pursues an understanding of the atomic structure of matter by way of simple mathematical properties of symmetry. This search evokes and helps resolve ancient philosophical disputes. The development of physics reveals at the same time a succession of true theories that nevertheless become ""closed off"" as new phenomena are discovered which have to be ordered by means of new, more abstract concepts. In art, as in science, Heisenberg discerns a striving for abstraction and through it a search for a basis for life common to all persons. Besides, a sense of beauty plays a decisive role in scientific explanation. All these themes converge in an optimistic and perhaps a bit naive prognosis. Heisenberg feels that soon the days of scientific specialism will be over. In every field we are compelled to look out across the frontiers. The coming unification of science will bring us closer to a unified humanity responsible for life on spaceship earth.