ORYZA2000: modeling lowland rice is the next in a series of (lowland) rice growth simulation models developed by IRRI and Wageningen University and Research Centre (WUR) in the early to mid-1990s in the project "Simulation and Systems Analysis for Rice Production (SARP)." It is an update and integration of the models ORYZA1 for potential production, ORYZA_W for water-limited situations, and ORYZA-N for nitrogen-limited production. Since the release of these models, new insights into crop growth and water-balance processes have been gained, new scientific subroutines developed, and programming standards and tools improved. These developments warranted a new release in the ORYZA series. Besides the scientific and programming updates, ORYZA2000 contains new features that allow a more explicit simulation of crop management options, such as irrigation and nitrogen fertilizer management. It can also be used in application-oriented research such as the design of crop ideotypes and the analysis of yield gaps to the optimization of crop management, the ex ante analysis of the effects of climate change on crop growth, and agroecological zonation.