What it is
STANAG 4728 is a NATO Standardization Agreement on system life cycle management. It is not a technical specification. It is the agreement by which NATO nations commit to ratify and implement two Allied Publications: AAP-20, Edition C, the NATO Programme Management Framework (also called the NATO Life Cycle Model), and AAP-48, Edition C, NATO System Life Cycle Processes, both built on the basis of ISO/IEC 15288. The life cycle principles and process detail that a reader usually wants live inside AAP-20 and AAP-48 themselves, not inside this short cover. Read on its own, STANAG 4728 requires almost nothing of a supplier directly. Its obligations run to nations, and it reaches a contractor only indirectly, once a nation has implemented it and a contract or tender names AAP-20 or AAP-48.
Who it binds, and how
STANAG 4728 is explicit that it binds nations rather than organisations. Its letter of promulgation describes the enclosed agreement as one which has been ratified by member nations, as reflected in the NATO Standardization Document Database (NSDD), and promulgated on that basis. Ratification and implementation are separate steps, and the document invites nations that have not yet reported their position to advise the NATO Standardization Office of their intention regarding ratification and implementation. So "is STANAG 4728 mandatory" has no single answer: it depends on whether a given nation has ratified and implemented it, and, for a supplier, on whether a specific contract invokes AAP-20 or AAP-48 as a result. The agreement takes effect upon receipt for use by the participating nations and NATO bodies, and it names no separate NATO Effective Date of its own.
What the agreement actually commits nations to
The stated aim is to respond to a single interoperability requirement: to implement harmonised system life cycle management principles in national and multinational armaments programmes, so that armament systems and equipment meet the Alliance's interoperability needs. Under "Agreement," participating nations agree to implement AAP-20 and AAP-48. In response to the NATO Policy for System Life Cycle Management, C-M(2005)0108, this means applying the life cycle framework in armaments projects supporting NATO capabilities, with both publications required in their respective latest version. None of this is written as a duty on a supplier; it is a duty on the nation running the armaments programme.
A cover agreement, not the life cycle framework itself
A reader who only has STANAG 4728 in hand does not yet have a life cycle model to work to. The framework itself, and the detail of what a programme has to produce at each stage, is in AAP-20 and AAP-48. This document does settle one practical question for anyone working across both: where AAP-20 and AAP-48 conflict, AAP-20 has priority. Its "Other related documents" field also names STANREC 4808 (engineering in NATO programmes), AEP-67 and ALP-10, though as informative reading rather than content this STANAG requires anyone to implement.
Reporting and review
Allies and NATO bodies are required to report their implementation details through the electronic reporting tool; partner nations are separately invited to report their implementation details the same way, as a voluntary step rather than a mandatory duty. The STANAG itself is reviewed in accordance with AAP-03, with the result recorded in the NSDD, a check on whether the agreement is still current rather than an audit of any organisation. The agreement is supervised by the CNAD Life Cycle Management Group (AC/327, Working Group 1), and comments on it go to the NATO Standardization Office in Brussels. This is the third promulgated edition, superseding Edition 2, dated 16 October 2015.
What it does not cover
STANAG 4728 names no life cycle stage, deliverable or acceptance criterion of its own, and no assessment or certification scheme: the only stated check is that the agreement itself is reviewed periodically, not that an organisation or a product is certified. The substance a programme actually works to sits entirely in AAP-20 and AAP-48.