The urgent environmental challenges of the 21st century starkly reveal the interdependencies that underpin the 17 Sustainable Development Goals (SDGs), and the devastating consequences for life on this planet due to human-made environmental harm. This EVALSDGs Insight #14 looks at the urgent need to mainstream environmental sustainability in the evaluation of all interventions, even when environmental sustainability is not a stated goal. It shows that for the most part this is not happening, and provides some conceptual considerations and practical examples for addressing this so that evaluations, regardless of the evaluand, critically include environmental impact.