We survey the recent developments in the literature on corporate diversification. This literature is voluminous, diverse, and quite old. To make the task more manageable, we focus our attention on recent contributions to that subset of the diversification literature that is in our judgment most influential in setting the agenda for financial research. The study of diversification at the corporate level can be grouped into one of two bodies of literature: cross-sectional studies of the link between corporate diversification and firm value (i.e., the diversification discount) and longitudinal studies of patterns in corporate diversification through time. The prevailing wisdom among financial economists throughout much of the last decade has been that diversified firms sell at a discount and that the level of corporate diversification has been trending downward. However, recent research questions both these tenets and a number of studies now suggest that the diversification discount is either not due to diversification at all, or may be a result of improper measurement techniques. Furthermore, some researchers are now beginning to argue that previous attempts to assess changes in the levels of corporate diversification through time is also flawed as a result of biases built into the compustat database in combination with the use of noisy proxies for corporate diversification.