The OECD Entrepreneurial Ecosystem Diagnostics report introduces a novel framework and dataset to assess and compare entrepreneurial ecosystems across all 38 OECD countries. Rather than producing a single index to rank countries, the report adopts a multi dimensional approach based on three core components: inputs, outputs, and variation. Inputs cover ten essential elements-Institutions, Culture, Networks, Infrastructure, Markets, Finance, Knowledge, Talent, Leadership, and Intermediate Services-captured through composite indexes built from about 40 indicators drawn from OECD statistics and other sources. Outputs reflect entrepreneurial performance, with indicators such as startup rates and business survival. The variation dimension measures how entrepreneurship is distributed socially and regionally, with attention to inclusivity, particularly for women and distribution of startups across regions. Each dimension is tracked at three time points to monitor ecosystem evolution and progress. Designed as a policy support tool, the report provides robust, evidence based insights to identify systemic bottlenecks and guide national strategies. It aims at facilitating informed dialogue and targeted policy action to build dynamic and balanced national entrepreneurial ecosystems. Released as a pilot, this first edition lays the foundation for future iterations, with continued refinement of data and analytical depth to enhance its relevance and impact.