The concept of infinity has been for hundreds of years one of the most fascinating and elusive ideas to tantalize the minds of scholars and lay people alike. The theory of infinite sets lies at the heart of much mathematics, yet it has produced a series of paradoxes that have led many scholars to doubt the soundness of its foundations. The author of this book presents a popular-level account of the roads followed by human thought in an attempt to understand the idea of the infinite in mathematics and physics. In so doing, he brings to the general reader a deep insight into the nature of the problem and its importance to an understanding of our world.