The release of previously secret internal tobacco industry documents has given the public health community unprecedented insight into the industry's motives, strategies, tactics, and data. The documents provide information that is not available from any other source and describe the history of industry activities over the past 50 years. The documents show that the tobacco industry has been engaged in deceiving policy makers and the public for decades. This paper begins with a brief history of the tobacco industry documents and describes the methodological challenges related to locating and analyzing an enormous number of poorly indexed documents. It provides an overview of selected important findings of document research conducted to date, including analyses of industry documents on nicotine and addiction, product design, marketing and promotion, passive smoke, and internal activities. The paper concludes with a discussion of the implications of tobacco document research for public health and the application of such research to fields other than tobacco control.