This study examined racial/ethnic differences in the relations between three dimensions of parenting practices (harsh, lax, and warm parenting) and children's externalizing behaviors across European American, African American, and Latinx families. Participants included 221 mothers who identified as African American (n = 32), Latina (n = 46), or European American (n = 143). Mothers' self-rated and observer-coded harshness, laxness, and warmth, and their ratings of their 3-year-old children's externalizing behaviors (hyperactivity, aggression) were analyzed. Research Findings: Multiple regression analyses indicated some racial/ethnic differences in the relations between harsh and warm parenting and children's externalizing behaviors. The slopes of the relation between greater harshness and greater aggression and hyperactivity were more positive for European American families than for African American or Latinx families. The slopes of the relation between greater warmth and less aggression were more negative for European American and Latinx families than for African American families. Results indicated no racial/ethnic differences in the relation between laxness and externalizing behaviors. Practice or Policy: These findings suggest racial/ethnic differences in the relation between some parenting practices and externalizing behaviors, which have important implications in culturally sensitive clinical practice for different racial/ethnic groups. More research is necessary to replicate these findings, and to identify other parenting practices that may be more important in racial/ethnic minority families.