Clear and effective legislation is a prerequisite to move sustainable development from theory into practice. This paper develops a methodology to investigate how Italian regions use Strategic Environmental Assessment (SEA) and the procedures used in the European Union (EU) to pursue sustainable development of policies, plans, and programs (PPPs). This case study is at the Italian regional level, examined to identify flaws and areas for improvement for each regional legislative framework. For this purpose, we used criteria from international debates on sustainability assessments. Through statistical multidimensional analysis, we classified Italian regions with similar SEA legislation. We developed four taxonomies, based on: i) legislation and guidelines; ii) integration between SEA and PPPs; iii) sustainability goals; iv) technical organization; v) participatory organization; and vi) monitoring. Our findings suggest that Italian administrators should cooperate to improve legislation at the regional level. Acknowledging the institutioncentered nature of SEA, this methodology could support SEA development in European countries with diversified traditions.