Scientific research is often influenced by financial interests, political interests, or the personal career interests of the scientists involved. For instance, pharmaceutical giant Merck manipulated clinical trial data in order to make sure that these data confirmed the safety of one of its products (Vioxx), as this served the company’s short-term commercial interests. The latter is obviously unacceptable. But why exactly is it unacceptable? One way to account for this is on the basis of the full ideal of purity. According to this ideal, scientific decision-making should be pure, i.e. unaffected by financial interests, political interests, career interests, etc. Although this ideal is questionable in light of earlier philosophical work, a lot of people (including philosophers of science) still hold on to it, or to a less strict version of it. In part 1 of the book, it is argued that it is better to fully abandon the ideal of purity. In part 2, an alternative ideal to assess interest influences in science is proposed: the ideal of epistemic integrity. A new concept of epistemic integrity is spelled out and systematically defended. Furthermore, the new concept is not only used to analyze the Vioxx debacle, but also to identify unacceptable interest influences in aerospace science, climate science, and biology, and to explain why exactly these interest influences are unacceptable. These analyses demonstrate that the new concept of epistemic integrity is interesting and useful for philosophers of science, scientists, engineers, science policymakers, and anyone else concerned about the integrity of science.