In the study of political attitudes, political efficacy has been one of the most continuously examined constructs since researchers first introduced it in the 1950s. Campbell, Gurin, and Miller defined efficacy as the "feeling that individual political action does have, or can have, an impact upon the political process, that is, that it is worthwhile to perform one's civic duties" (1954, p. 187). Simply put, efficacy is citizens' perceptions of powerfulness (or powerlessness) in the political realm. Notwithstanding its importance, measurement problems continue to plague studies that use political efficacy. Despite attempts by researchers to correct this deficiency over a decade ago (Craig, Niemi, and Silver 1990; Niemi, Craig, and Mattei 1991), the literature abounds with an assortment of measures, allowing for scant comparison of effects among many valuable studies and little coherence in the field. Using empirical analysis, this article furthers the argument for a standard measurement of this vital concept. Specifically, analysis of 1992 and 2000 American National Election Studies (NES) data, as well as original experimental data, supports the conclusion of Niemi, Craig, and Mattei (1991) that four questions developed in the 1987 NES Pilot Study provide a reliable and valid measure of internal efficacy. The measure performs well in two largescale surveys, as well as for two different types of internal efficacy in an experimental setting. This consistency across methods indicates just how good the measure is. Standardizing the measure of internal political efficacy will (1) ensure that researchers are validly and reliably measuring the concept, (2)