This paper examines the phenomenon of partial retirement . Topics covered include: (1) the quantitative importance of partial retirement, (2) institutional constraints in addition to mandatory retirement which limit the opportunity to retire partially in the main job, (3) the effect of these constraints on the specification of the relevant structural equations in a life cycle retirement model, (4) the impact of standard explanatory variables on four outcomes -- complete retirement, partial retirement both in and outside the main job, and non-retirement, (5) the importance of partial retirement even for those who do not face mandatory retirement, are not covered by a pension and are healthy, (6) the sensitivity of results based on a dichotomous retirement variable to whether the partially retired are classified as retired or not retired. A number of studies have either treated partial retirement inappropriately or have adopted unrealistic assumptions about the opportunity set facing potential retirees. Our findings call their results into question.