A new cotton model (CPM - a Cotton Production Model) based on the agronomic and physiological research that produced the model GOSSYM was developed. This model uses object oriented design and separate hierarchies to represent plant parts and physiological processes. This separation has allowed a belt-wide and nationwide participation of modelers and cotton researchers. Scientists at different research sites (ARS and collaborating universities and institutes) work on individual processes such as photosynthesis, light interception, or carbon allocation without regard to the original model structure which remains structurally isolated and independent of the individual process objects. The flexibility of the approach and model design is demonstrated by contrasting two different carbon allocation methods and the simple changes required to validate the overall model. Our research shows that the new model provides modularity, mechanistic richness, and advantages in process evaluation previously unavailable.