A Farm Process (FMP1) has been developed for MODFLOW-2000 (MF2K). In FMP1, the simulation of irrigation water demand, surface- and ground-water supply, and in-excess farm net recharge is dynamically driven by crop water demand and irrigation efficiency. Crop water demand and in-excess farm net recharge are simulated using analytical solutions that respond to climate and changes in groundwater levels. The FMP1 can be linked to the Streamflow Routing Package (SFR1) to simulate routed surface-water deliveries. The FMP1 may also be coupled to the Multi-Node Well Package (MNW) to apportion farm-well pumping to multiple aquifers and to constrain pumping by defined heads. MF2K-FMP1 can be used to estimate un-metered historical pumpage, assess water rights issues or operational decisions, and simulate non-drought versus drought supply and demand strategies. Additional ‘processes’ have been included, including the simulation of Spanish-based western water law and a farm mass-balance of all flows into and out of a farm. MF2K-FMP1 has been used to simulate micro- and macro-agricultural settings in New Mexico and California with either individual farms or large-scale water accounting units (irrigation districts, water balance regions, etc.). The purposes for these models range from the legal requirement to quantify water allocations to water resources management analysis. Data input for forecasting models can be preprocessed using current climate and land-use models. Future advancements will be the linkage to other MF2K ‘processes’ and ‘packages’ (e.g., for solute transport, salinity management, unsaturated-zone storage), and to climate, land-use, and economic models.