Laboratory studies suggest that improved cooking stoves can reduce indoor air pollution, improve health and decrease greenhouse gas emissions in developing countries. This Abdul Latif Jameel Poverty Action Lab (J-PAL) study co-authored by Rema Hanna, Esther Duflo and Micheal Greenstone provide evidence, from a large-scale randomised trial in India, on the benefits of a common, laboratory-validated stove with a four-year follow-up. While smoke inhalation initially falls, this effect disappears by year two. The paper finds no changes across health outcomes or greenhouse gas emissions. Households used the stoves irregularly and inappropriately, failed to maintain them and usage declined over time. This study underscores the need to test environmental technologies in real-world settings where behaviour may undermine potential impacts.