The problem of unifying quantum mechanics and gravity in a single coherent theory represents an enormous obstacle to full understanding of the forces of nature. The mysterious M-theory has emerged as a likely candidate for such a unifying theory. Whether the "M" stands for marvel or matrix, magic or membrane, it is clear that this area of research is among the most exciting and most profound in all of science. Edward Witten, one of the world's boldest innovators in this field, provides insights into these extraordinary developments in a completely expository presentation. Students and researchers specializing in mathematics and physics will find this lecture especially appealing. However, because it is completely nontechnical, large parts of it can easily be appreciated by viewers with little or no scientific or mathematical training.