For the past 20 years, social scientists have devoted increasing attention to the links between type of postsecondary education received and socioeconomic inequalities. Borrowing the terminology of Charles & Bradley (2002), we refer to the forms of these connections as horizontal dimensions of education-based stratification. We review studies of how institutional characteristics (college quality and type) and college experiences (field of specialization, academic performance, and pathway) are related to labor market outcomes. We also discuss research that treats college quality and field of specialization as dependent variables influenced by gender, race, ethnicity, and socioeconomic status. Throughout, we assess alternative theoretical explanations for why and how these horizontal aspects of college education play a stratifying role. We also note methodological developments that raise questions about some of the effects. Mirroring the literature, we emphasize how horizontal dimensions of stratification at the postsecondary level relate to gender differences on both the labor market and education sides. We propose additional theoretical and empirical issues that research on horizontal stratification in postsecondary education should address.