The criminal doctrine of command responsibility has a rich legal history, which makes it a widely recognized, if unsettled, concept of international criminal law. This article focuses on a key element of command responsibility: the commander’s knowledge of a subordinate's crimes. This article argues that current customary law instructs to apply a standard of actual knowledge of the commander, rather than the lower standard of constructive knowledge. The article reaches this conclusion by observing the primary shaping factor of international law—State behavior. Through the example of six diverse legal systems, the article demonstrates how the approach of legislative, executive, and judicial behavior of various States indicate that constructive knowledge is not a valid basis for incriminating commanders under international criminal law. Finally, the article contemplates some implications for future command responsibility cases. The article submits that multinational tribunals and States seeking to apply command responsibility should stick to the standard of actual knowledge, which reflects customary law as it currently stands, rather than aspirational law that lacks the necessary legal basis. This is particularly important not only for avoiding legal wrongdoing, but for maintaining the legitimacy and integrity of the criminal process that are crucial for promoting accountability.