1 Using a Choice Experiment to Estimate Mexican Farmers’ Valuation of Milpa Diversity and Genetically Modified Maize: A Latent Class Approach Ekin Birol 1 and Eric Rayn Villalba 2 1 Department of Land Economy, University of Cambridge, UK. Email: eb337@cam.ac.uk 2 Department of Geography, University College London, UK. Email: erayn@ucl.ac.uk Paper to be presented at the Third World Congress of Environmental and Resource Economists July 3rd-7th, 2006, Kyoto, Japan Abstract: A milpa is a traditional intercropping system of maize, bean, and squash. Milpas are repositories of agrobiodiversity in México, not only rich in inter- and infra-crop species diversity, but also in landraces of maize, which are building blocks for future improvements in this globally important staple crop. Even though they are still widely cultivated across México, sustainability of milpa cultivation is threatened by farmers’ integration into labour and output markets and recently, by the flow of transgenic constructs from genetically modified (GM) maize varieties to landraces in milpas. In this paper a choice experiment is employed to investigate farmer valuation of agrobiodiversity in traditional milpa systems and the option to cultivate GM maize varieties in milpas. Data are collected from 414 farm households across three states of México, and analysed using the latent class model, which enabled identification of those