This lecture was presented as part of the University of Pennsylvania's "Year of Proof" program. Mr. Gladwell is the author of four books, including The Tipping Point: How Little Things Make a Big Difference (2000) and Outliers: The Story of Success (2008). All four books were New York Times Bestsellers. Gladwell's books and articles often deal with the unexpected implications of research in the social sciences and make frequent and extended use of academic work, particularly in the areas of sociology, psychology, and social psychology.