DescriptionTransformations in the media environment affect citizens' political knowledge and participation. The internet has changed the media environment dramatically in the past 15 years, and the web has become a significant source of political information for Americans. Many scholars studying the web and its impact on politics argue that because the internet enables Americans to retrieve news that can be ideologically tailored to fit their political preferences, the web causes a more polarized public, more partisan elections, and may impede deliberation, and overall has a negative effect of representative democracy. I disagree. Using panel survey data and an experimental design, I examine whether the same underlying mechanisms that allow citizens to sort themselves into highly customized information worlds also enable members of historically disadvantaged groups to more efficiently access information that pertains specifically to them and to their groups' political goals, thereby providing important political knowledge gains and improving the representativeness of American democracy. The three main research objectives of this dissertation are: (1) To examine whether race and ethnicity influence selective exposure to political information online; (2) To research how selective exposure affects voters' knowledge of candidates' policy positions; (3) To test the impact of a high-choice and diverse media environment on political polarization and the quality of the vote choice.