Physicists and mathematicians throughout the world are working on one of the most ambitious theories ever proposed: superstring theory. String theory, as it is often called, is the key to the Unified Field Theory that eluded Einstein for more than 30 years. Finally, the century-old antagonism between the large and the small - General Relativity and Quantum Theory - is resolved. String theory proclaims that all of the wondrous happenings in the universe, from the frantic dancing of of subatomic quarks to the swirling of galaxies, are reflections of one grand physical principle and manifestations of one single entity: microscopically tiny vibrating loops of energy, a billionth of a billionth the size of an atom. In this work, Brian Greene relates the scientific story and the human struggle behind 20th-century physics' search for a theory of everything. Through the use of metaphor and analogy, this work makes some of the most sophisticated concepts accessible, aiming to bring the reader closer to an understanding of how the universe works.