The Forest and Agricultural Sector Optimization Model with Greenhouse Gases (FASOMGHG) is a dynamic nonlinear programming model of the U.S. forest and agricultural sectors. The model solves a constrained dynamic optimization problem that maximizes the net present value of the sum of producer and consumer surplus across the two sectors over time. The model is constrained such that total production is equal to total consumption, technical input/output relationships hold, and total land use must remain constant. FASOMGHG simulates the allocation of land over time to competing activities in both the forest and agricultural sectors and the associated impacts on commodity markets. In addition, the model simulates environmental impacts resulting from changing land allocation and production practices, including detailed accounting for changes in net greenhouse gas (GHG) emissions. The model was developed to evaluate the welfare and market impacts of policies that influence land allocation and alter production activities within these sectors. FASOMGHG has been used in numerous studies to examine issues including the potential impacts of GHG mitigation policy, climate change, timber harvest policy on public lands, federal farm programs, bioenergy production, and a variety of other policies affecting the forest and agricultural sectors.