Lean Manufacturing is continuously transforming in the era of Industry 4.0, merging digital technologies with conventional manufacturing processes focusing on sustainability through Circular Economy principles. This evolution of Business Systems has led to the newly formulated term ‘Digital Green Lean’, which contains the synergy between Lean Manufacturing, Digital transformation, and Sustainability principles. The research is driven by the need for a maturity assessment for leadership and business culture, enabling companies using Lean Manufacturing principles to evaluate their readiness and alignment with the principles of Industry 4.0 and Circular Economy. Organizations must adapt their Lean practices to remain efficient, digital, sustainable, and competitive. Method/Findings – The article consists of a literature review on maturity assessment, with the keywords Industry 4.0, Circular Economy, Lean Culture, Lean Leadership, and theoretical development for the maturity assessment, including evaluation criteria. The assessment includes (1) three dimensions, ten subdimensions, and 38 systems for Digital Green Lean Business Culture and (2) four dimensions, 19 subdimensions, and 43 skills for Digital Green Lean Leadership, to be evaluated in a developed five maturity levels. Implications – This research includes the first development of a maturity prescriptive and comparative assessment for companies to assess, compare, and develop action plans in their Lean journey within the context of Industry 4.0, Circular Economy, Lean Culture, and Lean Leadership, as part of the new integrated Digital Green Lean (DGL).