This monograph examines factors associated with adults' nonparticipation in organized learning. A deterrent to participation is defined as a reason contributing to an adult's decision not to engage in learning activities. First, existing models and theories that attempt to explain participation behavior are described. These include three recent approaches that attempted to combine dispositional, situational, and environmental factors into composite models of participation: Rubenson's Recruitment Paradigm, Cross' Chain-of-Response Model, and Darkenwald and Merriam's Psychosocial Interaction Model. The literature review explores the effect on participation of demographic and nondemographic variables. Because the research shows that these variables of and by themselves are not deterrents to participation, the monograph explores the evolution and refinement of the factors affecting educational participation and concludes that (1) "deterrents" is a multidimensional concept encompassing clusters of variables; (2) these variables are influenced by the prospective learners' perceptions of their magnitude; and (3) the impact of these variables on behavior varies according to individual characteristics and life circumstances. The last section addresses strategies to overcome these deterrents, including specific examples of successful approaches to stimulating participation, particularly among reentry women, the elderly, the educationally disadvantaged, and rural adults. A nine-page list of references concludes the document. (SK)