National culture is being challenged as societies evolve from their homogeneous origins. The theoretical base of this study uses two cultural dimensions, individualism-collectivism (Hofstede, 2001) and high-and low-context cultures (Hall, 1976), to unpack the effects of national culture on social network sites (SNSs). This study explores cultural differences in SNS usage patterns employing multiple methods, a paper-and-pencil survey and a content analysis of SNS profiles of survey respondents. The final analyses include a survey with 602 SNS users (361 college students in the United States and 241 college students in Korea) and a content analysis of 151 online profiles (58 Facebook and 93 Cyworld profiles). The survey findings revealed that SNS relationship patterns replicated those of face-to-face, while reflecting users' cultural orientations. In the survey findings, members of collectivistic cultures maintained SNS relationships more tightly and narrowly. While indicating such closed SNS relationships, they also exhibited lower levels of amount of self-disclosure, higher levels of intimate and vulnerable self-disclosure, and a greater willingness of privacy sharing than members of individualistic cultures. More visually anonymous online profiles also led to their closed SNS relationships by requiring random visitors, including old friends, to attain supplementary information to identify the user. As interdependent entities, members of collectivistic cultures paid more attention to self-presentation behaviors than members of individualistic cultures. The effect of individuals' cultural attitudes on SNS usage was mostly reconfirmed in the comparison by nationality while providing evidence of the effect of national culture. In the findings of the content analysis, Cyworld users from high-context cultures adopted more indirect communication styles that represent high-context cultures than Facebook users who adopted more direct communication styles that represent low-context cultures. The evident influence of national cultures on SNSs suggests revisiting the cultural dimensions, individualism-collectivism and high-and low-context cultures, to explore how they may explain patterns specific to particular cultures. The findings also suggest that international versions of SNS services that may be developed with the assumption of homogenous global populations of users need to be designed with the consideration of how culture influences use and shapes SNS behaviors. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]