This chapter focuses on the land use assessment submodule C3IAM/EcoLa within the C3IAM framework, addressing the complex interplay between climate change and land use. The model integrates three core components: food demand, biophysical parameters of land production, and land use allocation. By minimizing total costs (including production, irrigation, land conversion, technological innovation, and carbon emission costs), it optimizes land resource allocation. The food demand module dynamically projects crop and livestock product needs based on population and income trends. The biophysical parameter module quantifies irrigation water requirements, crop productivity, and carbon density. Under constraints of food security, water availability, and policy regulations, the land allocation mechanism balances agricultural expansion with ecological conservation, enabling multiscenario analyses of climate policies on food supply and carbon emissions. Coupled with climate and economic modules, the model evaluates feedback effects of land conversion on carbon cycles, providing decision-making support for regional land planning and global climate governance to advance sustainable development goals.