Research on previously secret tobacco industry documents has grown substantially during the past decade, since these documents first became available as the result of private and governmental litigation and investigations by the US Congress and the US Food and Drug Administration. Complementary research on tobacco litigation testimony is now being conducted through the Tobacco Deposition and Trial Testimony Archive (DATTA) project. We obtained transcripts of depositions and trial testimony, deposition and trial exhibits, expert reports, and other litigation documents from law firms, court reporter firms, individual lawyers and witnesses, tobacco company websites, and other sources. As of 3 March 2006, the publicly available collection of DATTA (http://tobaccodocuments.org/datta) contained 4850 transcripts of depositions and trial testimony, including a total of about 820 000 transcript pages. Transcripts covered testimony from 1957 to 2005 (85% were for testimony from 1990 to 2005) given by more than 1500 witnesses in a total of 232 lawsuits. Twelve research teams were established to study the transcripts, with each team covering a particular topic (for example, the health consequences of tobacco use, addiction and pharmacology, tobacco advertising and promotion, tobacco‐product design and manufacture, economic impact of tobacco use, youth initiation of tobacco use, and public understanding of the risks of tobacco use and exposure to second‐hand smoke). The teams used qualitative research methods to analyse the documents, and their initial findings are published throughout this journal supplement.