Although the continuous circulation of information, news, jokes, and opinions is ubiquitous in the worldwide social network, the actual mechanics of how any single piece of information spreads on a global scale have largely remained mysterious. A major challenge lies in the difficulty of acquisition of large-scale data recording the diffusion of any particular single piece of information. This talk will focus on recent work tracing such processes through online traces of information spreading. I will survey a variety of computational (and not so computational) efforts to trace diffusion through networks. I'll then focus recent joint work with Jon Kleinberg and and Flavio Chierichetti on the reconstruction of the propagation of massively circulated Internet chain letters, like those opposing the start of the Iraq war, Women Against Sarah Palin, protests of funding cuts for NPR/PBS, among others. The propagation of these petitions does not fan out rapidly in the style of a small-world epidemic, but rather produces a narrow but very deep tree-like pattern. This observation suggests a new and more complex picture for the spread of information through a social network. Joint work with Jon Kleinberg and and Flavio Chierichetti.