Elementary actions online establish an individual's existence on the web and her/his orientation toward different issues. In this sense, actions truly define a user in spaces like online forums and communities and the aggregate of elementary actions shape the atmosphere of these online spaces. This observation, coupled with the unprecedented scale and detail of data on user actions on the web, compels us to utilize them in understanding collective human behavior. Despite large investments by industry to capture this data and the expanding body of research on "big data" in academia, gaining insight into collective user behavior online has been elusive. If one is indeed able to overcome the considerable computational challenges posed by both the scale and the inevitable noisiness of the associated data sets, one could provide new automated frameworks to extract insights into evolving behavior at different scales, and to form an altogether different perspective of aggregated elementary user actions. This thesis addresses this fundamental and pressing problem and offers a "gestalt computing" approach when studying complex social phenomena in large datasets. This approach involves extracting macro structures from aggregated user actions, finding their possible meanings, and arranging data in layers so that it is iteratively explorable. The dissertation includes three major sections; first modeling and prediction of diffusion of information by users on the social web; next, detection of topics promoted by user communities; finally, presentation of the gestalt computing framework through a methodology that uses graph theory, language processing, and information theory to provide a top-down map of group dynamics on social news websites. What we find is not only statistical significance in the extracted structure, but also that the results are meaningful to human understanding. The efficacy of the proposed methodologies is established via multiple real-world data sets. [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.]