WHAT is attention? Can we measure it? How should we measure it?Attention is one of those concepts that are difficult to define,harder to measure, and impossible to do without. Attention is a concept that appears in most areas of communication research (sometimes lurking behind other equally bothersome pseudonyms, such as involvement, elaborative processing, effort, and interest). Because of its ubiquity, we have become accustomed to dealing with a variety of conceptual and operational definitions of attention. This cornucopia of attention theory and measurement has been well reviewed elsewhere (Grimes & Meadowcroft, 1995) and is not the focus of this essay. Rather, w'e will examine closely one of these measurement tools', secondary task reaction times (STRTs), and the definitions and theoretical assumptions that accompany it. Our goals in this review are to investigate how STRTs have been conceptualized theoretically, to refine the conceptual definition, and to offer a new interpretation of what STRTs measure based on a l~mited-resource approach to television viewing.