Social psychological research on the self is culled to develop some basic theoretical propositions about social movement participation. It is suggested that the self (1) consists of a cognitive structure based on reflexive consciousness & the capacity for self-awareness, (2) is defined by its social & interpersonal connections, & (3) actively makes choices, controls its own responses, & takes responsibility for its own actions. The importance of factor 2 in determining whether one joins & remains a participant in a social movement is discussed, focusing on the interaction between participation & the individual need to belong. The mediating effects of social conditions, charismatic movement leaders, & individual personality differences in attachment/belongingness are also explored. Contributions of factor 3, representing the self's executive function, volition, or agency, are explored using experimental data. It is concluded that a social movement's ability to attract &/or retain members may lie in how well it addresses their individual needs for belongingness or volition. 32 References. K. Hyatt Stewart