Despite recognition of the harmful effects of common method bias (CMB), its causes, consequences, and remedies are still not well understood. Therefore, the purpose of this article is to review our current knowledge of CMB and provide recommendations on how to control it. We organize our review into five main sections. First, we explain the harmful effects of CMB (why it is bad). Second, we discuss the complexity caused by the fact that there are multiple sources of CMB, several of which are likely to be present in any study. Third, we present evidence that the conditions under which CMB is likely to occur are relatively widespread, and fourth, we explain why CMB is not easy to fix. Finally, we identify several avenues for future research. Expected final online publication date for the Annual Review of Organizational Psychology and Organizational Behavior, Volume 11 is January 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.