This document gives guidance for organizations on establishing a phased approach to implement an energy management system (EnMS). This phased approach is intended to support and simplify the implementation of an EnMS for all types of organizations, in particular for small and medium-sized organizations (SMOs). This document gives guidance on the use of twelve core elements with four levels of maturity for each element to establish, implement, maintain and improve an EnMS that results in energy performance improvement. It enables the user of this document to implement a phased approach to achieve a level of energy management appropriate to its objectives and to build a strong foundation which can subsequently be extended towards meeting the requirements of ISO 50001:2018. This document is consistent with ISO 50001:2018 but does not cover all of its requirements.