The literature provides conflicting assessments about how firms choose their capital structures, with the "tradeoff", pecking order, and market timing hypotheses all receiving some empirical support. Distinguishing among these theories requires that we know whether firms have long-run leverage targets and (if so) how quickly they adjust toward them. Yet many previous researchers have relied on empirical specifications that fail to recognize the potential impact of adjustment costs on a firm's observed leverage. Likewise, few researchers have incorporated the effect of share price changes on market-valued leverage. We estimate a relatively general, partial-adjustment model of firm leverage decisions, and conclude that firms do have target capital structures. The typical firm closes more than half the gap between its actual and its target debt ratios within two years. 'Targeting' behavior as opposed to market timing or pecking order considerations explains a majority of the observed changes in capital structure.