This chapter discusses fault, negligence and the reasonable person test contained within. We will build upon the observations of Chap. 1 and discuss how AI challenges our current understanding of fault. This will enable us to make the necessary subsequent step towards public international law and space law. The second part of this chapter will therefore look at the fault standard contained in the Liability Convention and the Outer Space Treaty. As there is no internationally accepted definition of fault in international law, we ought to investigate the question as to how fault in international law should be understood. In part three, this chapter will therefore try to explore how other international treaties deal with fault and argue that negligence is generally seen as one way to establish fault in domestic law and is a central element in many jurisdictions. The author therefore argues that it constitutes a general principle of law recognised by nations. This in turn will then allow us look towards public international law and space law and conclude with outlining the challenges that AI poses to our understanding of fault and how it could lead to the undesired consequences that a State might escape liability altogether under space law for damage in outer space when employing AI for their space applications.