Study Objectives: To determine the relative effectiveness and predictors of Cognitive therapy (CT), Behavioral therapy (BT), and Cognitive Behavioral Therapy (CBT) for Insomnia in older adults. Methods: In a registered clinical trial (NCT02117388), 128 older adults with Insomnia Disorder were randomized to receive CBT, BT, or CT. Insomnia Severity Index (ISI) score was the primary outcome. Sleep diaries, fatigue, beliefs about sleep, cognitive arousal, and stress were secondary outcomes. Split-plot linear mixed models assessed within and between subject changes in outcomes among the treatments. As a secondary analysis, we used linear regression to test predictors of insomnia symptoms improvement, including sleep diary measures, cognitive arousal, stress, beliefs about sleep, baseline ISI score, and age. Benjamini-Hochberg correction was applied. Results: All groups exhibited insomnia symptom reduction at post-treatment (CT: d=-2.53, p<.001; BT: d=-2.39, p<.001; CBT: d=-2.90, p<.001) and 6FU (CT: d=-2.68, p<.001; BT: d=-2.85, p<.001; CBT: d=-3.14, p<.001). There were no group differences in the magnitude of ISI improvement (padj=.63), response (padj>.63), or remission (ISI<8; padj>.27). All groups exhibited significant improvements in secondary outcomes at post-treatment (padj <.05) and 6FU (padj<0.05). At post-treatment, the CT and CBT groups showed greater reductions in beliefs about sleep than the BT group (FInteraction(2,185)=5.99, padj=.03), and the CBT group showed a greater time in bed reduction than the CT and BT groups (FInteraction(2,185)=7.05, padj=.01). Baseline ISI was the only treatment predictor (b=1.95, padj<.001). Conclusions: CBT-I and its components each independently result in significant improvements in subjective insomnia symptoms, beliefs about sleep, worry, and fatigue in older adults.