This International Standard specifies the minimal requirements for the structure and contents of an assurance case. An assurance case includes a top-level claim (or set of claims) for a property of a system or product, systematic argumentation regarding this claim, and the evidence and explicit assumptions that underlie this argumentation. Arguing through multiple levels of subordinate claims, this structured argumentation connects the top-level claim to the evidence and assumptions. Stakeholders can evaluate the assurance case to determine the extent of achievement of the top-level claim by the system or product and whether this achievement is shown within the allowable uncertainty or risk and any related consequences. The results regarding the top-level claim and its support along with related uncertainties and consequences constitute a basis for rationally managing risk, achieving grounds for appropriate confidence, and aiding in decision making.