Since the early ‘90s, environmental NGOs have been fighting to be granted standing in actions for annulment. Direct access to the EU judiciary is hindered by the narrow interpretation given by the Court of the ‘individual concern’ requirement laid down under Article 263(4) TFEU. This narrow interpretation is known as ‘the Plaumann test’. By drawing from the literature on legal mobilisation and combining doctrinal and qualitative methods of analysis, the present dissertation explores how the European environmental movement has mobilised to overcome Plaumann in the last thirty years. In this regard, this thesis provides an empirical and theoretical contribution to the study of strategic litigation in the environmental domain. This by shedding light on the NGOs’ understanding of the legal opportunity structure in the EU, as well as on NGOs’ resources and legal strategies deployed to overcome Plaumann. This dissertation shows the relevance of networks membership in EU environmental litigation and argues that the lack of internal legal expertise does not necessarily prevent environmental organisations from resorting to legal mobilisation. Furthermore, this dissertation holds that, despite Plaumann, NGOs’ achievements are remarkable. In particular, the new Aarhus Regulation is expected to bring more legal mobilisation in Europe and deliver more disputes on the ‘science’ underlying EU environmental measures. Conversely, in the climate domain, NGOs are building what I conceptualised in terms of ‘transnational incremental judicial comfort’. The spreading of ‘judicial comfort’ in the climate context casts shadows on the CJEU, which looks increasingly ‘obsolete’ in the eyes of climate litigants. Finally, this dissertation argues that there is a demand within the European environmental movement for a different kind of EU environmental justice, which does not settle for administrative review of EU acts, but that rather strives for a more substantive judicial review of EU policy measures (including legislative acts).