This study assesses whether gender-based differences in political knowledge primarily result from differences in observable attributes or from differences in returns for otherwise equivalent characteristics. It applies a statistical decomposition methodology to data obtained from the 1992-2004 American National Election Studies. There is a consistent 10-point gender gap in measured political knowledge, of which approximately one-third is due to gender-based differences in the characteristics that predict political knowledge, with the remaining two-thirds due to male-female differences in the returns to these characteristics. The methodology identifies the relative contribution of the predictors of political knowledge to each portion of the gap, and then uses this information to elucidate the underlying sources of the political knowledge gender gap and its prognosis. Education is the characteristic that most clearly enlarges the gap, with men receiving significantly larger returns to political knowledge from education than women. Group membership reduces the gap as women obtain gains in political knowledge from belonging to organizations that do not accrue to men. However, these gains are not sufficient to significantly reduce the gap.