John Burdon Sanderson Haldane was a giant among men. He made major contributions to genetics, population biology, and evolutionary theory. He was at once comfortable in mathematics, chemistry, microbiology and animal physiology. But it was his belief in education that led to his preparing his popular essays for publication. In his own words: "Many scientifi c workers believe that they should confine their publications to learned journals. I think that the public has a right to know what is going on inside the laboratories, for some of which it pays." So begins Haldane's collection of essays, perhaps the most public intellectual communicating science before the writings of Stephen Jay Gould.