The energy efficiency first (EE1 st) principle is a key element of the recast Energy Efficiency Directive that emphasises the prioritisation of energy efficiency measures in all energy planning and investment decisions. However, regional authorities often face challenges in putting the EE1 st principle into practice, integrating it into regional energy strategies and balancing it with other energy-related needs. To address these challenges, the REGIO1st project, co-funded by the LIFE programme, focuses on raising awareness of the EE1 st principle among regional governments and their agencies, and providing them with the necessary tools and guidance to integrate this principle into their energy planning and decision-making processes. A key feature of the project is the development of the REGIO1st Planning Framework. This framework is a comprehensive toolkit for integrating the EE1 st principle into regional energy planning. It outlines a structured approach with different stages, each equipped with specific Excel and text-based tools. These tools facilitate data collection, stakeholder engagement, cost-benefit and multi-criteria analysis, ensuring a comprehensive planning process. The framework and its tools will be made available online in the first quarter of 2024, ensuring easy accessibility and usability. Currently, the REGIO1st Planning Framework is being applied in six European pilot regions. The pilots not only test the usefulness of the framework, but also adapt it to different regional contexts, demonstrating its versatility and effectiveness in practice. This paper introduces the REGIO1st Planning Framework, exploring its purpose, methodological foundations, structure and the variety of practical tools it offers. It also discusses its current application in pilot regions, highlighting how it supports regional authorities in integrating the EE1 st principle into their regional energy strategies.