Short sale constraints in the aftermarket of initial public offerings (IPOs) are often used to explain short-term underpricing that is subsequently reversed. This paper shows that short selling is integral to aftermarket trading and is higher in IPOs with greater underpricing. Perceived restrictions on borrowing shares are not systematically circumvented by “naked” short selling. Short sellers, on average, do not appear to earn abnormal profits in the near term and our findings are not driven by market makers. Short selling in IPOs is not as constrained as suggested by the literature, implying that other factors may be responsible for underpricing.

Using a complete record of U.S. over‐the‐counter (OTC) secondary trades in corporate bonds, we estimate average transaction costs as a function of trade size for each bond that traded more than nine times between January 2003 and January 2005. We find that transaction costs decrease significantly with trade size. Highly rated bonds, recently issued bonds, and bonds close to maturity have lower transaction costs than do other bonds. Costs are lower for bonds with transparent trade prices, and they drop when the TRACE system starts to publicly disseminate their prices. The results suggest that public traders benefit significantly from price transparency.

Given the complex and controversial nature of short-selling regulation, we review the academic literature and provide insights for policy makers and academics. We organize the complex history of short-selling regulation into three areas: trading restrictions, securities lending regulations, and disclosure requirements. We identify, analyze, and discuss 45 distinct regulations promulgated from 1896 to 2021, primarily by reviewing the academic literature and the data sources employed. We provide several insights regarding the effectiveness of regulatory approaches and the wider impact of short-selling regulation on markets.