David Baltimore begins the series of interviews describing his interest in biology as a high-school student and throughout his college years at Swarthmore. During college, he spent a summer at Cold Spring Harbor where he met Cy Levinthal and Salva Luria, both of whom encouraged him to go to graduate school at MIT. As an undergraduate, Baltimore held an interest in viruses. Knowledge and study of animal virology were still very limited, and when he decided to devote his PhD thesis to this topic, he moved to Rockefeller University to join Richard M. Franklin who was working with mengovirus. In his graduate work, he discovered that cultured animal cells infected with mengovirus synthesized an enzyme that catalyzed the synthesis of viral RNA. This was the first example of a virus coding for an RNA-dependent RNA polymerase. He then began working with poliovirus, work that continued for many years. In 1965, Renato Dulbecco asked Baltimore to join him at the Salk Institute for Biological Studies. There he initially focused on the replication of poliovirus RNA. With Mike Jacobson, a graduate student, he also began studying viral protein synthesis. Their work contributed to the recognition of the importance of proteolytic processing in the synthesis of eukaryotic proteins. Baltimore left the Salk Institute after two and a half years and returned to MIT in 1968 as an Associate Professor of Microbiology. He continued to focus his research on poliovirus, but also began work on vesicular stomatitis virus [VSV]. He and his wife, Alice Huang, who at the time was a research associate in his lab, discovered that VSV carried an RNA-dependent RNA polymerase within the virus particle. This work provided the insight that led to his discovery of reverse transcriptase—the enzyme in retroviruses that transcribes DNA from RNA—and won Baltimore the Nobel Prize for Physiology or Medicine in 1975 along with Howard Temin and Renato Dulbecco. Baltimore's work with retroviruses was the beginning of his interest in and work on cancer and tumor biology. In the mid-1970s, Baltimore expanded his research interests into the field of immunology, specifically into the areas of B cell development and antibody diversity. Baltimore concludes the interviews with a discussion of the discovery of reverse transcriptase, and thoughts on his research on poliovirus, retroviruses and immunology at MIT in the 1980s.