The Whole of Government (WG) approach is increasingly seen as an imperative for delivering coherent and integrated policies, joined up and seamless services, and integrated program management in government. Although no generic WG framework currently exists, there are reported cases of WG initiatives by different governments. Grounded in existing theories, frameworks and cases related to inter-organizational collaboration, collaborative Electronic Government (EGOV) and joined-up government, this article describes how to build a collaborative IT Strategy Management (ITSM) environment based on the WG approach. The article first develops a WG model to identify the enabling elements for the WG approach. Next, it identifies the necessary conditions for creating a collaborative ITSM environment in government, applies the WG model to synthesize a set of generic requirements for implementing the WG approach, and presents a WG ITSM toolset to support the implementation. Finally, the generic WG-ITSM requirements are used to analyze a case study involving the WG-ITSM development in a city government. Based on the case study, the validity of the WG model and generic WG-ITSM requirements as well as the usefulness of the toolset are discussed. The article closes with the recommendations for the WG-ITSM practice and for further development of the WG framework.