Topology is the only major branch of modern mathematics that wasn't anticipated by the ancient mathematicians. Throughout most of its history, topology has been regarded as strictly abstract mathematics, without applications. However, illustrating Wigner's principle of “the unreasonable effectiveness of mathematics in the natural sciences,” topology is now beginning to come up in our understanding of many different real world phenomena. In this minisymposium, Robert MacPherson describes the history and pervasiveness of topology, Raúl Rabadán describes how topology modifies our understanding of evolution and disease, and Randall Kamien discusses the relationship between topology and liquid crystals, like those in computer displays. Following the presentation, Robbert Dijkgraaf moderates a panel discussion on topology.