This paper examines empirically what factors contribute to voluntary adoption of the ISO 14001 environmental management system by farmers. The adoption model incorporates the expected profitability of implementing the standard and investigates the impact of prior knowledge on the probability of adopting, by jointly considering two information measures: a “reported information” indicator and an “estimated knowledge” score. A Probit regression is applied to 2000 original survey data on French farmers. The analysis suggests that while the expected profitability of implementing the standard is a significant determinant of adoption intentions, real and perceived prior knowledge plays a strong and potentially counterintuitive role.