Abstract: With social networking site (SNS) use now ubiquitous in American culture, researchers have started paying attention to its effects in a variety of domains. This study explores the relationships between measures of Facebook use and political knowledge levels using a pair of representative samples of U.S. adults. We find that although the mere use of Facebook was unrelated to political knowledge scores, how Facebook users report engaging with the SNS was strongly associated with knowledge levels. Importantly, the increased use of Facebook for news consumption and news sharing was negatively related to political knowledge levels. Possible explanations and implications are discussed.