Aliens are big in America. Whether they've arrived via rocket, flying saucer, or plain old teleportation, they've been invading, infiltrating, or inspiring us for decades, and they've fascinated moviegoers and television watchers for more than fifty years. About half of us believe that aliens really exist, and millions are convinced they've visited Earth. For twenty-five years, SETI has been looking for the proof, and as the program's senior astronomer, Seth Shostak explains in this engrossing book, it's entirely possible that before long conclusive evidence will be found. His informative, entertaining report offers an insider's view of what we might realistically expect to discover light-years away among the stars. Neither humanoids nor monsters, says Shostak; in fact, biological intelligence is probably just a precursor to machine beings, enormously advanced artificial sentients whose capabilities and accomplishments may have developed over billions of years and far exceed our own. As he explores what, if anything, they would tell us and what their existence would portend for humankind and the cosmos, he introduces a colorful cast of characters and provides a vivid, state-of-the-art account of the past, present, and future of our search for extraterrestrial intelligence.