This guide provides a management framework and actionable recommendations for cross-border interoperability between national Single Windows, bilaterally or multilaterally. This guide builds upon UN/CEFACT Recommendation 36 and develops a five-pronged management framework for Single Window interoperability (SWI). In addition to actual business needs for SWI, four critical areas for successful implementation of SWI are proposed and discussed in detail, further elaborating on guidelines included in the Recommendation 36. In this guide, these areas are referred to as the four levels of interoperability, i.e., policy and legal interoperability, people and organizational interoperability, process and data interoperability, and platform and technical interoperability. Descriptions and recommended actions are provided for each of these five issues. As defined in chapter 1, the scope of SWI in this guide is regulatory and cross-border in nature. As a consequence, the SWI initiative must be a collaboration effort mainly between government agencies in the participating countries. When the business needs/objectives for SWI are mutually agreed on, the SWI that will be created must have the ability to electronically exchange information between disparate and diverse ICT-enabled SW facilities. The identification of business objectives and the enablers or the critical success factors for achieving these objectives are summarized as follows: (a) Business needs. This comprises the capture, analysis, evaluation and agreement on business needs as the primary driver for cross-border SWI by including perspectives from public and private stakeholders in trade by the participating countries; (b) Policy and legal interoperability. This involves securing the highest-level political commitment between or among the participating countries for collaboration in establishing cross-border SW interoperability. It also covers the enactment of related laws and regulations related to mutual recognition of electronic data exchanges across borders; (c) People and organizational interoperability. This includes the establishment of an intergovernmental governance and management structure among the participating countries, with mandated directives and supporting resources. This also covers building and improving people capacity to cope with new technology, innovation and change related to cross-border SWI; (d) Process and data interoperability. This comprises the analysis of the current/as-is processes, design and agreement on better target/to-be processes related to information exchange across borders. It also covers analysis, harmonization and agreement on better to-be standardized data and documents in electronic form for exchange across the borders of the participating countries; (e) Platform and technical interoperability. This covers the analysis, design and agreement on several necessary set of common platform and technical aspects, e.g., interface specifications and common ICT infrastructure if needed, so that different SW facilities can connect and communicate with each other. The recommended actions are discussed in detail in chapter 3 and summarized in the annex. Chapter 4 provides details and options for specific issues, e.g., legal issues, connectivity options and interface protocol specifications. This guide also suggests a governance and management structure as well as phase-by-phase programme management for governing and managing the establishment of cross-border SWI. The three main phases for governance are evaluating, directing and management monitoring. The other four phases of management include planning (including designing to-be, and possibly proof-of-concept development), building, operating and monitoring. Chapter 5 discusses these phases in the context of programme/projects life cycle in detail.