The three rules of epidemics -- The law of the few: connectors, mavens, and salesmen -- The stickiness factor: Sesame Street, Blue's Clues, and the educational virus -- The power of context (part one): Bernie Goetz and the rise and fall of New York City crime -- The power of context (part two): the magic number one hundred and fifty -- Case study: rumors, sneakers, and the power of translation -- Case study: suicide, smoking, and the search for the unsticky cigarette -- Conclusion: focus, test, and believe.