This study extends Arriaga et al.’s (2018) model of attachment-security enhancement to group relationships, examining if social groups can bolster attachment-insecure members’ felt security (confidence that support will be available when needed). Groups providing acceptance and support (safe context) and reinforcing competence and autonomy (positive models of self) are hypothesized to mitigate attachment-anxious members’ worries and enhance felt security. In addition, groups that respect the need for self-reliance (softening context) and promote enjoyable interdependent interactions (positive models of others) could alleviate attachment-avoidant members’ defensive detachment. The research comprises six studies. Study 1 develops a new scale for security-enhancing provisions within groups and correlates it with felt security. Studies 2-5 involve laboratory experiments manipulating one security-enhancing provision to assess its impact on felt security and related cognitive or behavioral correlates. Study 6, a longitudinal study of adolescents in group therapy, investigates the effects of perceived security provisions on their felt security and emotional/behavioral outcomes over four months.