Unions represent millions of workers in both Britain and the U.S. despite substantial membership declines over the last thirty years. Union influence and trends contained therein are major concerns to a broad range of social sciences and business-related disciplines, as well as to unions themselves. Data on unions as organizations are, however, woefully inadequate for the purpose of assessing the activities and influence of unions, as well as their status and prospects. In this article, we assess what we know and do not know about unions as organizations, and offer suggestions for what we need to know and how to get from where we are presently to where we would like to be.