Prior studies suggest that large book-tax differences (BTDs) are associated with future earnings changes or earnings persistence. The literature has explored a number of potential explanations for this relation, without a clear answer emerging. To integrate the various assertions I divide total BTDs into temporary and permanent categories and hypothesize that temporary BTDs (reflected in deferred taxes) predict future changes in pretax earnings, whereas permanent BTDs predict future changes in tax expense. The results are consistent with these hypotheses. Prior studies also suggest that both types of BTDs are associated with earnings management and tax avoidance. I find evidence that tax avoidance firms have a more positive association between their BTDs and both pretax earnings changes and tax expense changes. However, I find only inconsistent evidence on the influence of earnings management on the association of the components of BTDs and future earnings changes, with results dependent on the research design. Overall, the evidence suggests that while tax avoidance and earnings management may contribute to the association between BTDs and future earnings changes, there are also more fundamental drivers of this association.