Drawing on a representative survey sample of just over 2,500 young adult respondents between the ages of 18 and 35 from across the USA and Canada, our study seeks to understand who exactly takes part in organized and digital nonbelief activities. Our findings show that (a) there is a positive association between religious childhood socialization and the likelihood of being involved with organized and digital atheist, humanist and secularist activities among young adult nonbelievers; (b) there is a positive link between involvement in organized and digital nonbelief activities and those who experience discrimination due to their nonbelief, mediating the religious childhood socialization association (subcultural identity theory); and (c) there is a remaining positive direct relationship between religious childhood socialization and involvement in organized and digital nonbelief activities as individuals seek to retain some vestiges of religious life among these nonreligious groups (vestiges of religious life theory). We additionally demonstrate that, while fewer than half of nonbelieving Millennials are involved in organized or digital nonbelief settings, those in the USA are more likely to be involved than in Canada. Moreover, in both nations, those who are involved tend to be more engaged in online settings versus in-person contexts. Wilkins-Laflamme and Thiessen: Religious Socialization and Millennial Involvement in Organized and Digital Nonbelief Activities Art. 2, page 2 of 15 Additionally, our study goes further than simply providing this first series of important descriptive estimates. We also develop a better understanding of who these individuals are, including their demographics and (non) religious backgrounds, by teasing out key socialization factors that are tied to adult involvement in organized and digital atheist, humanist and secularist activities. Our study addresses the following key research questions: To what extent are organized and digital nonreligious activities more appealing to nonbelievers who come from more religious backgrounds? Are nonbelievers who experienced a religious socialization growing up more likely to face discrimination, and respond to it by taking part in atheist, humanist and secularist activities and spaces? Are they also seeking vestiges of their previous religious community life in these nonreligious groups, minus God? Nonreligious Organizations, Embattled Narratives and Community Seeking From their own publicly available materials, as well as a number of qualitative field studies conducted by researchers in the USA and Great Britain especially, a richer profile and understanding of atheist, humanist and secularist organizations has developed over the last two decades. There is diversity among these organizations' positions and goals. Some groups, particularly staunch atheist groups, take a confrontational posture towards religion. Areas of foci include "religious criticism, critical thinking, intellectual stimulation, and advocacy of science or church-state separation m...