Government institutions, courts and administrative tribunals have been entrusted with making critical decisions concerning environmental risks. The nature of these decisions and their underlying uncertainty inevitably involve reliance upon opinion evidence from environmental scientists. This analysis begins with a review of the evolution of scientific expert opinion as an evidentiary input to legal decision-making followed by the identification of problems arising with scientific evidence based upon those problems identified by the authors and/or reported in the literature. These problem issues were organised under five categories or 'interfaces' for both environmental trials and administrative hearings, being: the quality of scientific information introduced; the communication and comprehension/understanding of scientific information; scientific uncertainty; the use of scientific information to establish and enforce decision-making standards; the suitability of existing legal decision-making institutions and legal procedures for resolution of scientific issues in environmental decision-making. Finally, unique empirical research was conducted by performing a questionnaire survey with parallel questions on 93 problem issues identified under these five interfaces. The survey was completed by 18 judges (90% response), 63 tribunal members (40.6% response), 101 lawyers (6.1% response) and 107 expert scientific witnesses (30.9% response), who had actually participated in environmental trials and administrative hearings across five jurisdictions. The differing perspectives of these groups on several issues serve to highlight many of the fundamental incompatibilities that currently exist between science and the law in relation to environmental decision-making. Eighteen recommendations are offered to address the range of problem issues identified and discussed.