This thesis examines asset pricing and capital structure of small- and medium-sized enterprises (SMEs) in three essays. Firm finance and asset pricing are areas of voluminous research in the literature. Most of this research observes firms trading on public stock exchanges. In my thesis, I examine privately-owned SMEs where relatively little research has been done. I use a proprietary database of over 16,000 SMEs that sold from 1990 to 2010, reporting market valuations and accounting information. My findings contribute to the literature on asset pricing and capital structure of private firms that benefits researchers, entrepreneurs, investors, and analysts.The first essay examines whether the size effect in returns found in traded stocks is present in SMEs. The size-effect literature generally observes listed firms and finds that smaller firms tend to have higher returns. Using the SME database, I document the size effect in private firms using market valuations. I also find the size premium is concentrated in smaller SMEs. In firms smaller than $2.5 million in market value, the size effect is nearly 13 times stronger compared to larger firms.The second essay explores the effects of investor sentiment and marketwide liquidity in SME returns. Prior studies find these factors have effects in returns of listed firms. I find that SME returns are negatively related to sentiment and liquidity. As sentiment or liquidity rise, SME returns tend to fall. This study also finds that the effects of sentiment and liquidity are concentrated in smaller firms and weaken or disappear in larger SMEs. Apparently investors in smaller SMEs are more influenced by sentiment and liquidity. I also find that sentiment and liquidity have conditional effects on the magnitude of the size premium. The third and final essay examines SME capital structure. Firm capital structure has been one of the most contentious issues in finance theory for over 50 years. Relatively little research examines private firm finance and no previous studies to my knowledge have examined SME capital structure using market-based leverage ratios. I examine relations between leverage and capital structure determinants suggested by theory using market-based and book-value leverage ratios. I find support for both the trade-off and pecking-order theories. This study also finds that SMEs tend to use short-term debt much more than long-term debt and firms appear to practice maturity matching where managers tend to match borrowing terms with asset life. Evidence also suggests that capital structure determinants suggested by theory have greater explanatory power for market-based leverage ratios than for ratios based on book values.