The environmental issue, increasingly central in contemporary legal and political discourse, challenges traditional constitutional paradigms and demands a reconfiguration of legal systems in light of transnational and intergenerational concerns. In the Italian context, environmental protection has progressively gained constitutional relevance, reflecting both cultural shifts and normative evolution within the legal order. This article examines the multifaceted impact of environmental values on modern legal systems through a tripartite analytical framework. First, it explores the doctrinal and jurisprudential developments that have contributed to the constitutionalization of environmental protection in Italy, culminating in recent constitutional reforms. Second, it assesses the role of supranational sources, primarily European Union law and international environmental law, in shaping national environmental policies and in embedding principles such as sustainable development, the precautionary principle, and the duty of non harm into domestic legal systems. Third, the article offers a comparative analysis of constitutional models in selected European jurisdictions, namely Spain, Portugal, Germany, and France, as well as emerging global trends in climate litigation, highlighting the growing judicial engagement with environmental claims. The study underscores how environmental law is not only reshaping substantive legal norms but also redefining the scope and function of constitutional democracies.