It has long been suggested that environmental assessment has the potential to contribute to sustainable development through mechanisms above and beyond informing design and consent decisions, and while theories have been proposed to explain how this might occur, few have been subjected to rigorous empirical validation. This research advances the theoretical debate by building a rich empirical understanding of environmental assessment's practical outcomes, from which its potential to contribute to sustainable development can be gauged. Three case study environmental assessment processes in England were investigated using a combination of data generated from content analysis, in-depth interviews, and a questionnaire survey. Four categories of outcomes are delineated based on the research data: learning outcomes; governance outcomes; attitudinal and value changes; and developmental outcomes. The data provide a robust critique of mainstream theory, with its focus on design and consent decisions. The article concludes with an examination of the consequences of the context-specific nature of environmental assessment practices in terms of developing theory and focusing future research.