Reviews programmatic studies of resistance during parent training therapy, including a brief description of a procedure developed at the Oregon Social Learning Center for coding resistant behaviors. Analyses of sequential interactions during treatment of 70 preadolescent boys and girls show that therapists’ efforts to intervene produced immediate parental resistance (PR). From baseline to midtreatment phases, there were increases in the therapists’ efforts to intervene, which were accompanied by increases in PR. Contextual variables such as parent pathology also correlated with higher levels of PR. Decreases in PR were associated with improvements in parental discipline practices. PR altered the behavior of the therapists, reducing their effectiveness. A regression analysis shows that improvements in discipline predicted fewer future arrests and out-of-home placement.