The field of metamaterials arose from a deepened understanding of how electromagnetic waves interact with materials and subwavelength-scale scattering structures. The exploitation of these more-complex material-wave interactions has generated much global research activity. We can, in principle, engineer materials to greatly extend the selection of those currently available. This Tutorial Text presents the electromagnetic properties of both naturally occurring and manmade materials, focusing especially on structured or engineered metamaterials. After a review of Maxwell's equations and material properties, the concepts of resonant meta-atoms and composite media are introduced. The fabrication of metamaterials and the properties of negative-index materials are explained. The difficulties associated with reducing the size of meta-atoms for use at optical frequencies are described, and the use of metamaterials for superresolution imaging is presented in some detail.