Abstract: This paper explores the empirical relationship among insider trading law, other legal rules and institutions, and equity markets in an international context. In particular, using legal and economic data from a cross-section of countries, I investigate two empirical relationships: the relationship between insider trading law and ownership concentration and the relationship between insider trading law and equity market liquidity. Consistent with agency theories which predict that the ability of insiders to engage in uninhibited trading encourages concentrated share ownership, I find that tougher insider trading laws are negatively and significantly related to the degree of ownership concentration in publicly traded companies. That is, in economic regimes where insider trading is more stringently regulated, large shareholders hold a significantly lower fraction of outstanding shares. In addition, consistent with market microstructure theories of the relationship between asymmetric information and trading costs, I find that weaker insider trading regimes have, on average, less liquid equity markets. It is hoped that the findings of this paper will inform the ongoing law and economics debate over the desirability of regulating trading by corporate insiders.