Analysis of national election surveys from 1956 to 1968 reveals significant changes in the voters' perceptions of issues and the major parties. There has been a considerable increase in the correlation of party identification and opinion on six major issues, relating to social welfare, racial integration, and foreign aid. Voters are more prone to see a difference between the parties on these issues and are increasingly likely to identify the Democratic party as favorable to federal governmental action. These findings contrast with those ofThe American Voterand similar studies. The reasons for the changes cannot be found in demographic factors, as tested by controls for age cohorts, education, region, and race. More probably the explanation lies in strictly political factors. A particularly important event was the presidential campaign of 1964, in which ideological differences between the parties were deliberately emphasized. The electorate responded to this campaign by becoming more ideologically aware, and its learning appears to have persisted through the 1968 election. This finding suggests that past conclusions about the low ideological awareness of the electorate were specific to the Eisenhower era, and that the issue content of the vote will vary with the stimuli provided by the general political environment.