Research Findings: A total of 81 children participated in a longitudinal investigation of inhibitory control (IC) from 2 to 4 years of age. Child IC was measured via maternal report and laboratory measures under conditions of conflict and delay. Performance on delay IC tasks at 3 years was related to performance on these same tasks at 2 and 4 years, but performance on conflict IC tasks was not related over time. Delay IC task performance was concurrently related to conflict IC task performance in 3- and 4-year-olds but was not related in 2-year-olds. Measures of IC varied in their associations with measures of verbal ability and maternal-report IC. Such findings highlight important similarities and distinctions between conflict and delay IC abilities in their relation to one another and to temperament and language over time. Practice or Policy: Studies of IC and related concepts reveal that children who are regulated enjoy school more and have higher school competence, particularly in mathematics and reading achievement. Because conflict IC and delay IC show unique patterns of development over time, educators can expect classroom behaviors drawing on the state-like conflict IC to show more fluctuation over time than those drawing on the trait-like delay IC.