Emerging self-regulation skills were assessed in 407 low-income African American and Latino (primarily Mexican-origin) preschoolers. A battery of self-regulation tasks was administered when children were 2½ years old and again approximately 1 year later. Confirmatory factor analyses supported four components of self-regulation: inhibitory control, complex response inhibition, set shifting, and working memory. Complex response inhibition was too rare a skill in this sample to be detected reliably from measures collected at 2½ years of age, but it emerged from measures collected at 3½ years. In addition, significant ethnic differences were found in that African American children scored better on measures of complex response inhibition and set shifting, whereas Latino children scored better on measures of inhibitory control and working memory. Implications of study findings for measuring self-regulation in low-income ethnic diverse populations of young children, as well as for developing interventions to enhance self-regulation development, are discussed.