This dissertation investigates the economics of health behaviors. It focuses on the ways health behaviors, specifically smoking and fertility, respond to economic factors such as price and income, as well as non-economic factors such as health-related knowledge and health policy. The first chapter, "The effect of contraceptive knowledge on fertility: the roles of mass media and social networks," explores the effect of contraceptive knowledge on fertility using an instrumental variables approach. It draws upon the "Knowledge, Attitudes, and Practice of Contraception in Taiwan" (KAP) dataset and focuses on the period when Taiwanese family planning programs were in effect. The results indicate that mass media and social networks play This study finds that important roles in disseminating contraceptive knowledge. women transform their knowledge into behavior"that is, contraceptive knowledge reduces fertility, no matter which fertility metric is measured (life-time fertility or probability of giving birth). The second chapter (coauthored with Donald Kenkel), "U.S. cigarette demand: 1944 - 2004," uses data from 23 national cross-sectional surveys conducted by the Gallup Poll from 1944 through 2004 to investigate the changes in cigarette demand in the United States from the 1940s through 2004, individual and government attitudes toward smoking changed dramatically. It estimate standard two-part models of cigarette demand as a function of demographics, income, and cigarette prices. The results show that from 1944 to 2004: the gender difference in smoking rates almost disappears; the black-white difference reverses; a strong gradient with schooling emerges; and the negative income elasticities strengthened in magnitude. The third chapter, "WTO Entry, a New Cigarette Tax Scheme, and the Tobacco Market in Taiwan," analyzes the impacts of Taiwan's entry into the WTO, which was accompanied by a series of policy changes on both the supply and demand sides of the tobacco market. It investigates the link between cigarette tax and price by imputing the tax pass-through rates, and confirms the hypothesis that free trade induces an increase in advertisements and the introduction of new brands and products. Regarding smokers' reactions to price changes, this study finds some evidence that smokers not only react to price changes, but also react to relative price changes by switching brands. It also takes into account other scenarios accompanying the WTO entry that influence the brand choices.