Focusing on the model excluding past behavior (Model 1), intention, action planning, and habit at follow-up were statistically significant direct predictors of social distancing behavior, with effect size for intention and habit generally larger in the U.S. sample. PBC directly predicted behavior in the Australian sample only, also with a small effect size. Intention predicted action planning in both samples with large effect sizes. Subjective norm, moral norm, and PBC predicted intention in both samples, with small-to-medium effect sizes, but effects of attitude were not significant. There was a small effect of anticipated regret on intention in the U.S. sample only. Habit at baseline predicted habit at follow-up in both samples, with large effect sizes. There was also a small-sized effect of habit at baseline on intention in the U.S. sample only. Overall, the model accounted for significant variance in social distancing behavior (Australian sample, R2 = .198; U.S. sample, R2 = .361), intentions (Australian sample, R2 = .571; U.S. sample, R2 = .623), and habit at follow-up (Australian sample, R2 = .416; U.S. sample, R2 = .486). Intentions (Australian sample, R2 = .066; U.S. sample, R2 = .148), action planning (Australian sample, R2 = .029; U.S. sample, R2 = .044), and habit at follow-up (Australian sample R2 = .041; U.S. sample, R2 = .129) each accounted for substantive variance in behavior. Action planning significantly moderated the intention–behavior relationship in the Australian sample only. While the effect was not in the predicted direction, probing the interaction revealed that the intention–behavior relationship increased as the level of planning increased, consistent with theory. However, the intention–behavior relationship is more likely to be smaller at lower levels of planning, and it seems that planning makes less of a difference when the intention–behavior relationship is large. A plot of the interaction effect is presented in Supplementary Appendix F.