The colossal magnetoresistive (CMR) oxide materials derive their remarkable properties from an unusually strong interaction among magnetic ordering, elec­ tronic transport, and crystal structure. In simplified terms, the large magnetoresis­ tance stems from a magnetically driven insulator-metal transition. The electronic and magnetic properties, and, thus, the CMR behavior, are determined by the chemical composition and crystal structure. Thus, an understanding of the way composition and structure affect transport and magnetism guides the search for new CMR compounds. Additionally, measurements that probe the interactions between the crystal structure and magnetism or transport provide unique insight into the underlying physics of these materials.