Detecting and punishing violations of research integrity requires first having to prove them. However, establishing proof of research misconduct presents a number of challenges. Firstly, it has to be conducted in a variety of contexts, including before research integrity officers, university disciplinary committees, civil courts, criminal courts, at first instance and on appeal. In each of these instances, the rules of evidence have their own specific features. Secondly, it may be necessary to prove not only material facts, but also circumstances that are more difficult to grasp, such as intention or negligence. In addition, not all evidence is admissible, as it may breach a duty of fairness or protected secrets. Consequently, research integrity officers and judges may be unable to consider all relevant evidence when assessing allegations of misconduct. This article examines the legal issues pertaining to the proof of research misconduct, based on French law and the law of the European Convention on Human Rights. This article examines the burden of proof, the object of proof, the admissibility of evidence and the exclusion of evidence. It identifies the differences in evidence that exist depending on whether investigations into research misconduct are conducted before research integrity officers or before the courts. It analyses the justifications for these differences and concludes that the role of research integrity officers should not be confused with that of judges, even if this leads to differences in the proving of research misconduct.