Midway through this set of learned essays by the late nuclear physicist and Nobel laureate Werner Heisenberg, one finds the statement: ""It would be simplest of all to say that a proton just consists of continuous matter. . . . The difference between elementary and composite particles has thus basically disappeared. And that is no doubt the most important experimental finding of the past fifty years."" Such an assertion should trigger a frisson of awe or delight in even the most unsophisticated reader. The point of this collection is that language inevitably shapes the questions asked in science. The long tradition from Democritus has led to the search for the fundamental particle, the ultimate constituent of matter. The question is meaningless, Heisenberg asserts, and refers to the history of quantum mechanics, high-energy experiments, and his own Uncertainty Principle as evidence. These essays begin with a deceptive simplicity but move quickly into the abstractions of theoretical physics. A few, recollections of the early days and encounters with Einstein, are more accessible. They give the flavor of the foment of 20th-century physics and suggest the fundamental differences between the statistical approach of the quantum physicists and the ""God does not play dice"" philosophy of Einstein. Heisenberg's metaphysics and his explorations into the intuitions of creative physicists in formulating ""closed systems"" make him more akin to Plato than to Aristotle: the Really Real may be the idea, the abstraction. Heisenberg was a greatly gifted man of strong opinions. He clearly maintains that all who are bent on the pursuit of quarks or partons as the ultimate particles are doomed since the pursuit is meaningless. In spite of thorny areas, the book should appeal to those interested in fundamental questions of metaphysics and the nature of creativity, as well as to physicists and historians of science.