New and innovative approaches are necessary to confront the current biodiversity crisis, especially when it comes to protecting endangered species, which are at the most immediate risk of extinction. In this thesis, I explore whether lawsuits using the precautionary principle may represent an effective species conservation strategy by examining how judges in the United States, Canada, and Australia are using the principle to protect endangered species. This study addresses a gap in international environmental law (IEL) and species conservation literature by explicitly investigating the linkage between the precautionary principle and endangered species litigation. Through qualitative analysis on 36 cases from the United States, Canada, and Australia, I suggest that judges perceive a role for the precautionary principle in endangered species lawsuits, that they derive more authority for the principle from domestic rather than international law, and that the Canadian judiciary is uniquely receptive to legal strategies linking the principle with endangered species.