In recent years, Twitter emerged as an important news driver as most major news organizations now provide newsfeeds via Twitter. We classified 34 South Korean news outlets based on the pattern of co-following among 709,586 Twitter users. We also had a rare opportunity to match their following behavior with individual-level attributes by relying on supplementary survey data on 1,811 members of an online survey panel. Our results reveal that partisan and generational selectivity sharply polarizes news following on Twitter, suggesting that Twitter is likely to reinforce the existing political divisions in society by reducing the likelihood of chance encounters with the disagreeable views. (Author abstract)