A study investigated characteristics of retirees and types of voluntary groups they joined after retirement. Data were collected through face-to-face interviews and completed questionnaires of 206 Australians over age 50. Five categories of voluntary organizations were studied: intellectually challenging, sporting/exercise, social, helping others, and hobby clubs. Data indicated joining groups was influenced by gender, age cohort, level of education, past employment, health status, and familial status. Males were more likely to join sporting groups, and slightly more likely to join groups for intellectual challenge and to be of help to others. Females were more likely to join for social contact and to pursue hobbies. Increasing age led to an overall decreasing tendency to belong to groups, and membership of groups for social purposes increased with age. Those with higher levels of education were likely to join groups offering intellectual challenge and "helping others" activities; those with lower levels tended to take part in more passive activities; and hobby and craft groups attracted people from all educational backgrounds. Participants from white-collar occupational backgrounds had a higher tendency to join groups, and those who joined clubs to help others were predominantly from these backgrounds. Health status did not affect membership, except among older seniors. For older adults who lived alone, social contact may have been a major incentive to join. (Appendixes contain 24 references, 13 charts, and the instrument.) (YLB)