Secure attachment relationships have been described as having a regulatory function in regard to children's emotions, social cognition, and behavior. Although some theorists and researchers have argued that attachment affects children's self-regulation, most attachment theorists have not strongly emphasized this association. The goal of the current meta-analysis was to determine the magnitude of the relation between attachment security status and effortful control (EC)/top-down self-regulation in children up to 18 years of age. One hundred six papers met the inclusion criteria and 101 independent samples were used in analyses. When secure attachment status was compared with insecure attachment status, a significant relation (effect size ES) with EC favoring children with a secure attachment was found (100 studies; 20,350 participants; r = .20). A stronger relation was found when the same coder evaluated attachment than when the coder was different and when the measure of attachment was continuous; other moderators were not significant. Securely attached children were higher in EC than their avoidant (r = .10) or resistant (r = .17) counterparts. Children with organized attachments were higher in EC than those with disorganized attachments (r = .17), although this finding could be due to publication bias. For some comparisons of subgroups (B vs. A, B vs. C, and/or D vs. all others), moderation was found by source of information (higher ES for same reporter), age at assessment of EC and/or attachment (higher ES at older ages), method of attachment (lower ES for observational measures), time difference between assessments or research design (higher ESs for smaller time differences and concurrent findings), and published versus unpublished studies (higher ES for unpublished studies for A vs. B). Public Significance Statement A modest, positive relation between quality of children's attachment and their top-down self-regulation (effortful control) was found. This finding is consistent with the conclusion that efforts to improve the quality of the parent-child attachment might foster children's effortful self-regulation, although it is also possible that children's top-down regulation affects the quality of their attachment or both aspects of functioning are affected by a third variable, such as genetics or maternal sensitivity. Moderational analyses also suggest that attachment quality is associated with top-down self-regulation to a greater degree for older than younger children, although this finding may be due in part to how attachment has been assessed at different ages. Thus, it is important in future work to learn more about how the mode of assessing attachment affects the relation of attachment quality to other variables such as top-down self-regulation.