This articles studies the salience of the generational cleavage in European party systems. European electorates have become more evenly divided between generational cohorts due to population aging. Since 1980, the share of Europeans over 65 years has grown from 12% to 20% and the median age has increased from 31 to 45. The article analyzes whether population aging is driving a structural, behavioral or political realignment based on a generational cleavage. Structural realignments are driven by the changing composition of the electorate (i.e., population aging). Behavioral realignments are due to changing voting patterns among groups (i.e., age determining vote choice). Political realignments involve changing turnout rates between social groups (i.e., young people abstaining more). The sample integrates survey data from the ISSP, ESS, WVS and EVS, including over 1 million respondents from 636 surveys of 31 European countries. The analysis measures the Lambda index for the salience of age groups in vote choice for each survey. The results are consistent with political realignments: population aging is strongly associated with a growing turnout gap between younger and older voters due to increased abstention among the young.