The following article is based on the plenary presentation given by Darryl L. Smith ofLos Alamos National Laboratory on December 1, 2003, at the Materials ResearchSociety Fall Meeting in Boston. The presentation contrasted the electronic structure ofinorganic semiconductors with that of organic semiconductors, examined how thedifferences in electronic structure lead to complementary physical properties, anddiscussed applications of these materials-including infrared detectors and sources,gamma-ray detectors, and chemical/biological sensors-that are of interest to issues ofnational security.