The digital era has ushered in a new collective action landscape that scholars are now trying to

understand. To date, there has been insufficient attention paid to cross-national variation collective action that is driven by digitally mediated thin tie networks rather than formal political organizations. In this dissertation, I propose a theory of cross-national variation in digitally networked collective action (DNCA) and test it empirically through a paired case comparison of Japan and South Korea. I argue that the extent and scale of DNCA is to a large extent a function of citizenship norms, such that the use of digital media and related technologies will have a more transformative effect on collective action in contexts with high aggregate levels of engaged norms, and a less transformative effect in countries with low aggregate levels of engaged norms. I test this theory by looking for differences in the extent to which digitally mediated thin ties, social network size, and social network heterogeneity are conducive to participation in protests, boycotts, and petitions in Japan and South Korea. I evaluate the external validity of the results of the main analyses through a larger-N analysis.