The multiple pathways linking 4-year-olds' self-regulation to their adjustment (defined as teacher-reported socioemotional functioning and academic achievement) among a sample of children from ethnically and geographically diverse low-income families (Time 1 N = 163) were examined at two time points over the transition from preschool to first grade. Self-regulation was defined in terms of attentional and behavioral regulation and inhibitory control. Three research questions were investigated in separate papers. In all analyses, demographic factors such as maternal age, education, workforce entry, family income category, and child age were statistically controlled. In the first paper, I investigated whether self-regulation mediates the relationship between caregivers' limit-setting practices and children's adjustment. Findings indicate that the extent to which children were able to engage in attentional and behavioral forms of regulation fully explained the relations between limit-setting practices and early reading achievement in first grade. Contrary to hypotheses, attention and behavior regulation did not mediate the effect of limit-setting on children's socially competent, externalizing, and internalizing behaviors. In the second paper, I tried to explicate the known relations between inhibitory control and adjustment by examining the mediating role of behavior regulation measured longitudinally at Time 1 and concurrently at Time 2. Support was found for the mediating role of behavior regulation in the relations between inhibitory control and children's reading and writing achievement. Comparable support was not found for children's socioemotional outcomes. Limited support was detected for the indirect effect of inhibitory control through behavior regulation on social competence, but only for children from married families at Time 1. In the third paper, I examined whether negative emotionality (defined as anger/frustration) moderated the relationship between self-regulation and child adjustment. Results suggest that negative emotionality moderated the relationship between attention regulation and children's reading grades: Children with fewer attention regulation skills and higher levels of frustration received lower reading grades compared with peers who also displayed few attention regulation skills but were low in frustration at Time 1. Contrary to predictions, the paths from behavioral regulation to achievement did not vary as a function of child frustration. For all three papers, policy implications are discussed.