Rationale: Although many additive manufacturing systems are based heavily upon the principles of Computer Numerical Control (CNC), the coordinate systems and nomenclature specific to CNC are not sufficient to be applicable across the full spectrum of additive manufacturing equipment. This International Standard expands upon the principles of ISO 841 and applies them specifically to additive manufacturing. Although this International Standard is intended to complement ISO 841, if there should arise any conflict, it is this International Standard shall have priority for additive manufacturing applications. For any issues not covered in this International Standard, the principles in ISO 841 may be applied. This second edition of ISO/ASTM 52921 replaces first edition (ISO/ASTM 52921:2013), which has been technically revised. The main changes compared to the previous edition are as follows: Terms and definitions that are included in ISO/ASTM 52900:2019 Additive manufacturing! General principles Fundamentals and vocabulary have been removed from this document and instead referred to ISO/ASTM 52900; Since the list of terms and definitions have been removed from this edition, it is therefore not a standard terminology anymore, and therefore it has been renamed so that the title describes the actual content of the standard; The remaining normative content of the document including the annex have been consolidated into one single normative document; Specifications of some aspects of initial build orientation and orthogonal orientation notation have been integrated in the text body of the document; The coordinate system for additive manufacturing with horizontal z-positive build direction is described and illustrated.