Background Structured training in research integrity, research ethics and responsible conduct of research is one strategy to reduce research misconduct and strengthen reliability of and trust in scientific evidence. However, how researchers develop their sense of integrity is not fully understood. We examined the factors and circumstances that shape researchers’ understanding of research integrity. Methods This study draws insights from in-depth, semi-structured interviews with 33 researchers in the life sciences and medicine, representing three seniority levels across five research universities in (...) Switzerland. Results The results of this study indicate that early education, moral values inculcated by the family and participation in team sports were the earliest influences on notions of honesty, integrity and fairness among researchers. Researchers’ personality traits, including degree of ambition and internal moral compass, were perceived as critical in determining the importance they attributed to conducting research with high ethical standards. Positive and negative experiences in early research life also had a significant impact on their views regarding research integrity. Two thirds of the study participants had not received any formal training in research integrity. Their awareness of training opportunities at their institutions was also limited. Conclusion Age-appropriate development of honesty and integrity starts as early as primary education. Research integrity training should be offered from the bachelors level and continue throughout the entire professional life of researchers. Although these courses may not imbue researchers with integrity itself, they are essential to improving the research culture, reinforcing integrity norms, and discouraging researchers who lack personal integrity from engaging in research misconduct. (shrink)