COMPASS is a package of coupled models of the land surface, including the Variable Infiltration Capacity (VIC) macroscale land surface energy and water balance model, and newly developed models of sub-surface flow and solute transport, runoff routing and floodplain inundation, sediment transport, and carbon chemistry in particulate and dissolved forms (the new ROMBUS model). The interface between the different COMPASS component models is modular so as to allow advances in models or alternate models to be introduced easily, or alternatively, to replace interactive models with prescribed values. This interface has the potential to be expanded in the future to include land-atmosphere coupling, as well as models of the biosphere (including vegetation dynamics, phenology, and photosynthesis and respiration). A primary use for COMPASS, among other possible uses, is the simulation of carbon fluxes in the dry and wet surface environments, and ultimately the return of carbon to the atmosphere. Of special interest is the use of scenarios to evaluate the influence of land-use change patterns, such as large-scale conversion of forested land to pasture or irrigated crops, on hydrological, sediment, and carbon fluxes. Application of COMPASS to parts of the Amazon and the Mekong is described. More information will be provided at http://www.hydro.washington.edu/Lettenmaier/Models/COMPASS/