Disputes involving an environmental component continue to be at the forefront of ongoing legitimacy debates in investment treaty arbitration. Critics of the international investment regime contend that arbitration favors the property rights of foreign investors over the need of host states to environmentally regulate and legislate in the public interest. While there is some doctrinal and anecdotal evidence to this effect, we ask whether investment treaty arbitration as a whole is as problematic for domestic environmental protection as has been perceived. With mixed method techniques, we analyze environmental cases in the context of five specific legitimacy concerns. Overall, we find that critiques of the system require nuance and clarification of the normative benchmarks for legitimacy assessments. In a number of important areas, the critiques do have purchase but in the aggregate, the most problematic cases are often successfully defended by respondent states.