Disciplines are revolutionized by the development of novel tools: the telescope for astronomers, the electron microscope for biologists, the particle accelerator for physicists, and brain imaging for cognitive psychologists. Social media provide a high-powered lens into the details of human behavior and social interaction that may prove to be equally transformative for the social sciences. Until recently, social and behavioral scientists have had to choose whether to rely on direct real-time observation of very small numbers of non-representative individuals (e.g. in field observation or in the laboratory) or to rely on atomized retrospective accounts obtained through survey responses from large representative samples. Social media offers us the opportunity for the first time to do both - to observe human behavior and interaction in real time and on a global scale. Recent projects in the Social Dynamics Laboratory at Cornell have used nearly complete national telephone logs to test Granovetter's theory of "the strength of weak ties," hundreds of millions of tweets to track diurnal, weekly, and seasonal mood changes across diverse cultures, Egyptian Twitter messages to track protest mobilization during the Arab Spring, and global email logs to test Huntington's theory of the "Clash of Civilizations." These studies illustrate the limitations and challenges of online analytics but also the potential for a relational revolution in the study of human behavior and social interaction.