["Symbolic Interaction, EarlyView. ", "\nBoundary‐work describes the activities of social groups as they seek to differentiate themselves from others to establish credibility, authority, or to protect their interests. While a growing body of literature explores occupational boundary‐work in health care, limited research has focused on how lay actors practice boundary‐work online. This study draws on 18 months of qualitative research from a comparative internet ethnography of two Facebook “mom groups”—one “science‐based,” the other “natural”—to examine how mothers with ideologically divergent concepts of health engage in boundary‐work. I find that both groups used a common set of strategies including gatekeeping, identifying legitimate knowledge, dichotomous “othering,” and policing. However, tactics differed. While the science group emphasized rationality, scientific/medical authority, and exclusion, the natural group prioritized epistemic pluralism, personal health agency, and inclusion—differences that mirror occupational boundary‐work between biomedicine and holistic medicine in health care. Situating these findings in the context of intensive and neoliberal mothering, I argue that maternal boundary‐work is a response to the pressures of contemporary parenting. Through boundary‐work, mothers align themselves with concepts of ideal mothering while distancing themselves from perceived inferior approaches. I conclude that insofar as these strategies are inherently individualist, they do little to ameliorate collective problems faced by mothers and their families.\n"]