This chapter examines what is known about employee age and the effectiveness of job behaviour, concentrating on studies carried out in work settings and linking those with laboratory investigations. Rated job performance is shown to be in general unrelated to age; overall absenteeism tends to be greater among younger employees; accidents are more common at lower ages; and staff turnover declines with age. A framework is proposed in terms of three main components of job behaviour: physical ability, adaptability and general work effectiveness. The major practical need is seen to be the implementation of procedures which enhance among older employees the second of those components. An outline model is suggested, with the objective of identifying those jobs in which greater age is either a benefit or a limitation. That model indicates that, in research as well as in practice, the key issues now concern the nature and enhancement of adaptability.