Abstract: This dissertation addresses three questions relating to mergers. Chapter 1 investigates the proper measurement of efficiency gains through mergers. Chapter 2 analyzes the dynamic relationship between repeat acquirer activities and market responses, and Chapter 3 analyzes leading theories of mergers where mergers are classified very broadly. The anomalies literature suggests that pricing is biased systematically for securities grouped by certain characteristics. If these characteristics are related to selection in an event study sample, imprecise predictions of an event study method may produce erroneous results. In Chapter 1, I perform simulations to compare a battery of event study prediction and testing methods where samples are grouped by market equity, prior returns, and valuation ratios. Significant statistical errors are reported for both standard and newer methods, including three and four factor models. The best procedure is found to be the Fama-French three factor model tested with a sign statistic. Chapter 2 addresses the dynamics of repeat acquirers. Prior studies have shown that repeat acquirers' early abnormal returns are higher than the returns from later acquisitions. Using new econometric techniques with a panel dataset over two decades, I find that this pattern of declining returns is not caused by market anticipation of later deals. Instead, announcement returns are deal-specific, rather than firm-specific, and thus provide valuable feedback to acquirers about their M&A choices. In a novel approach, I find that firms consider this feedback when making current decisions, providing new evidence of learning in M&As. Finally, I find that as larger firms demand larger targets of small relative sizes, returns decline. Finally, in Chapter 3, we posit that M&As should be defined to include mergers, acquisitions, alliances, joint ventures, and divestitures. This paper investigates the relative roles of the three competing explanations of M&As using our broad definition of M&As and finds strong support for the neoclassical theory over the redistribution and behavioral theories. This support is illustrated with a case study of the M&A activity of the top five U.S. defense contractors from 1990 to 2004.