This dissertation examines the consequences, measurement, and evolution over time ofcitizen knowledge of the Democratic and Republican parties’ positions on major policy issues. In the dissertation’s first paper (co-authored), we resolve a longstanding and central puzzle in the public opinion literature concerning the over-time instability of citizen issue attitudes—namely, is this instability the result of measurement error in surveys or is it in the opinions themselves? By leveraging for the first time the strong relationship between citizen knowledge of party issue positions and citizen issue opinion stability, the paper reveals that the erratic nature of policy attitudes through time reflects not measurement error but turnover in the opinions themselves. In the project’s second paper I experimentally test an alternative survey instrument for measuring citizen knowledge of the party’s issue positions. I find that the traditional measurement approach used in the U.S. context likely understates this knowledge among lower education survey respondents, indicating that this cohort’s democratic competence is somewhat higher than has heretofore been believed. In the project’s third paper I explore the evolution of party position knowledge in the U.S. mass public over time, and present evidence that this knowledge has spread a good deal since the 1970s. My findings indicate that, contrary to one prominent school of thought in the public opinion literature, the American public’s political belief systems have on average become better organized over the past fifty years, likely as a result of party elite polarization. Taken together, these papers demonstrate the key conceptual importance of placement knowledge in the study of public opinion, a status that has heretofore been largely unrecognized. The findings show that party placement knowledge should be placed center stage by public opinion scholars, alongside general political knowledge, if the field is to accurately grasp a host of central phenomenon such as the nature of issue attitudes, polarization, and the evolution of belief system organization over time.