This dissertation examines the law and economics of generic drug entry, and the problems that arise from specific U.S. regulatory arrangements that govern innovation and competition in the market for patented pharmaceuticals. As Chapter 1 explains, competitive entry by generic drug makers is limited by both patents and industry-specific regulation, which together provide the means for brand-name drug makers to avoid competition and thereby recoup large investments in research, development, and testing. At the same time, the complex rules of the Hatch-Waxman Act furnish a pathway by which generic drug makers may challenge the validity or scope of brand-name patents, with a view to entering the market with a competing product prior to patent expiration. The subsequent chapters examine several aspects of the competitive interaction between brand-name and generic drug makers. Chapter 2 analyzes settlements of patent litigation between brand-name and generic drug makers, in which the brand-name firm pays the generic firm in exchange for delayed market entry. Such pay-for-delay settlements are an important, unresolved question in U.S. antitrust policy. The analysis reveals that the pay-for-delay settlement problem is more severe than has been commonly understood. Several specific features of the Act—in particular, a 180-day bounty granted to certain generic drug makers as an incentive to pursue pre-expiration entry—widen the potential for anticompetitive harm from pay-for-delay settlements, compared to the usual understanding. In addition, I show that settlements are "innovation inefficient" as a means of providing profits and hence ex ante innovation incentives to brand-name drug makers. To the extent that Congress established a preferred tradeoff between innovation and competition when it passed the Act, settlements that implement a different, less competition-protective tradeoff are particularly problematic from an antitrust standpoint. Chapter 3 synthesizes available public information about pay-for-delay settlements in order to offer a new account of the extent and evolution of settlement practice. The analysis draws upon a novel dataset of 143 such settlements. The analysis uncovers an evolution in the means by which a brand-name firm can pay a generic firm to delay entry, including a variety of complex "side deals" by which a brand-name firm can compensate a generic firm in a disguised fashion. It also reveals several novel forms of regulatory avoidance. The analysis in the chapter suggests that, as a matter of institutional choice, an expert agency is in a relatively good position to conduct the aggregate analysis needed to identify an optimal antitrust rule. Chapter 4 examines the co-evolution of increased brand-name patenting and increased generic pre-expiration challenges. It draws upon a second novel dataset of drug approvals, applications, patents, and other drug characteristics. Its first contribution is to chart the growth of patent portfolios and pre-expiration challenges. Over time, patenting has increased, measured by the number of patents per drug and the length of the nominal patent term. During the same period, challenges have increased as well, and drugs are challenged sooner, relative to brand-name approval. The analysis shows that brand-name sales, a proxy for the profitability of the drug, have a positive effect on the likelihood of generic challenge, consistent with the view that patents that later prove to be valuable receive greater ex post scrutiny. The likelihood of challenge also varies by patent type and timing of expiration. Conditional on sales and other drug characteristics, drugs with weaker patents, particularly those that expire later than a drug's basic compound patent, face a significantly higher likelihood of challenge. Though the welfare implications of Hatch-Waxman patent challenge provisions are complicated, these results suggest these challenges serve a useful purpose, in promoting scrutiny of low quality and late-expiring patents.