This publication aims to critically compare the environmental standing to sue in Argentina and Italy with a special focus on the role of NGOs in the lawsuit. The text examines the European Union and the Mercosur environmental legislation and analyzes the effects of their implementation on Member States and associated members. It also focuses on other South American approaches such as the 2008 Ecuadorian Constitution that for the first time recognized constitutional rights to Nature as an autonomous legal subject. Furthermore, the text compares the environmental framework of the Argentinean and Italian Constitutions, exploring the new aspects introduced with their respective reform in 1994 and 2001. The work looks also at external related factors such as the influence that the US Supreme Court''s environmental jurisprudence had on the Argentinean Supreme Court. Finally, the text analyzes the environmental standing to sue regime of the two countries. In conclusion, it addresses a final remark relating to the introduction of the environmental class action as a legal tool to improve the current legal framework.