Trends in research on participation in adult education have reflected social changes, shifting from sociodemographic surveys toward emphasis on understanding motivation for participating. Participation has been studied primarily from the perspective of service providers, gathering data on participants or dropouts. Since the 1970s, researchers have shifted from a narrow preoccupation with participation in education to interest in participation in learning. Although research had been mainly descriptive, researchers seek now to explain adult participation. The descriptive studies have identified sociodemographic characteristics of participants in formal adult education, their motivations for attending classes, barriers or deterrents to their attendance, and characteristics and perspectives of "nonparticipants." The largely descriptive variables of previous studies (situational, institutional/environmental, and dispositional) are seen as interacting in complex ways to influence individual participation. Some comprehensive theories and models that have been developed to explain participation are as follows: congruence model; expectancy theory; expectancy-valence theory; chain-of-response model; psychosocial interaction model; and ISSTAL (Interdisciplinary conceptual framework, Sequential Specificity of relations, Time Allocation-Life span perspective) model of social participation. None of the theories is sufficient. Critical areas for future research are studies that place educational participation in the broader context of adults' life course, identify and document the influence of individuals' perceptions, and use qualitative methodology. (Contains 70 references.) (YLB)