This article examines the strategic legal activity of the environmental movement in the United Kingdom over the past twenty years. Environmental non-governmental organizations (NGOs) have increasingly turned to the courts in pursuit of their policy goals, despite significant losses on substantive legal issues, difficulties gaining standing and high costs awarded against them under the “loser pays” system. This presents a puzzle: why does the movement continue to pursue legal action in the face of what activists claim is a hostile legal opportunity structure (LOS)? This study explores this seeming paradox using a single-country, cross-temporal comparative approach, an original dataset of legal cases taken by NGOs as well as qualitative case studies of strategic litigation. It highlights the agency the movement exhibits within opportunity structures and suggests that NGOs that use litigation are able to highlight the failings of the existing system and improve future access to justice for themselves and other groups.