Large grant-making philanthropic foundations in the UK and the EU can have a significant influence over environmental law and as such are worthy of more attention from environmental law scholars. Through analysis of publicly available documents, we identify in this paper an absence of consistent transparency by these foundations. This makes their influence hard to understand, hard to research, hard even to see at work in the world. Transparency is complex and challenging, however. And so, rather than berating problematic approaches, we explore through interviews with actors in the field, as well as the academic literature, both the difficulties that foundations experience in pursuing transparent practices and the benefits of transparency. We conclude by identifying some principles for improved visibility of foundation work.