Cornell astronomer Harwit's theme is not so much the discoveries that astronomy has made but how they have been made. With what tools? When? By whom? His book is thus an excursion into the philosophy, politics, and sociology of astronomy and his aim is no less than a program for the future: How can we use the limited resources available (talent, tools, time, money) to promote new discoveries, to advance astronomical learning? Harwit enumerates many examples from the recent and distant past to illustrate that astronomical advances have often followed the introduction of a new tool (Galileo's spyglass, x-ray and radio astronomy); that innovators are frequently outsiders (all the early British radio astronomers were physicists); and that equipment developed for military use later sparks progress in astronomy (WW II rocketry led to the space program). This approach, plus Harwit's discussion of how astronomy progresses at both theoretical and analytical levels, provides the ammunition for his quite daring calculations of how many new phenomena in the universe remain to be discovered--several hundred, he contends. (The analysis is based on ingenious assumptions about the numbers of channels on which information can be transmitted, the nature of ""phenomena,"" whether some phenomena can be discovered on only one channel, etc.) And he follows this bravura performance with chapters describing astronomical discoveries in detail, thus providing a condensed history of astronomy along with the meta-astronomical ideas. Finally come the recommendations: upcoming astronomers should be trained in physics; midcareer training should be allowed for, so that new techniques can be picked up; innovation must be encouraged; funding should be stabilized; and the peer review system should be loosened up (to prevent the ""old boy"" closeout of wild young ideas). All this makes good sense--in any of the sciences--and the general public and policy-makers could benefit from such a view. But some of Harwit's colleagues may take offense at the frequent references to the usefulness of the military. . . and of innovators outside the astronomy mainstream. Challenging material--some sections appropriate for the general reader, some chiefly for specialists.