Globally, the imperative to integrate power grids is intensifying as renewable integration, extreme weather, and rapid electrification strain reliability and raise costs. Yet building inter-regional transmission is challenging: jurisdictions struggle to coordinate planning, allocate costs equitably, design trading frameworks, and secure community license. Europe, Australia, Canada, and the United States each face these pressures from different starting points, offering valuable lessons in both success and failure. This paper consolidates insights from more than one hundred interviews with grid operators, utilities, policymakers, and academics worldwide, alongside a review of international planning and regulatory processes. It identifies emerging best practices across five pillars: governance, planning, trading, financing, and community engagement. Case studies highlight how Europe and Australia’s structured planning processes, U.S. cost-allocation debates, and Canada’s Indigenous-led partnerships each illuminate different pathways to overcome barriers. By comparing diverse approaches, the paper distils strategies that have proven effective in advancing inter-regional transmission: transparent governance, harmonized planning, neutral trading interfaces, beneficiary-pays financing, and genuine community participation. These insights provide a roadmap for policymakers and system planners to accelerate grid integration, enhance resilience, and enable the clean energy transition.