Retirement is often concentrated at specific ages-in particular the 'normal retirement age' and an 'early retirement age'. Financial incentives cannot fully explain this. Moreover, the participation effect of a higher normal retirement age importantly exceeds the encompassing income effect. Based on a literature survey, we conclude that social norms, default options, and reference-dependent utility are likely explanations for the individual propensity to retire at specific retirement ages. Further empirical research on non-financial determinants of retirement is needed to fully understand individual retirement behavior.