A professor of zoology (insect biology), Alfred Kinsey (Liam Neeson), understands bugs but not himself. Finally marrying, he and his wife Clara McMillen (Laura Linney) discover that sexuality is more than watching bugs "do it".
He find himself stumped when asked by newly-wed students about an aspect of human sexual behavior. His scientific credibility is then brought to the study of sexuality, initially by analyzing a questionnaire given to his students. His wife suggests that the students might lie on a questionnaire, but be truthful if interviewed in person. Kinsey sets out to interview his students then later many thousands of people across America using a team of researchers from Indiana University, under a grant from the Rockefeller Foundation.
The 1940/50s McCarthyism creates fear, uncertainty and doubt in many regarding the study, including the Foundation and the University. Nevertheless, the resulting books on male sexuality (1948) and later female sexuality (1953), revolutionize how sex is perceived; and, the work laid the ground for the "sexual revolution" of the 1960s. During this, Kinsey and his team discover the wide range of 'acceptable' sexual behavior, and their own sexual freedom - sometimes to their dismay.