Crop models have been instrumental in predicting yields in wide ranges of current and future environmental conditions. However, they encounter problems in representing spatial heterogeneity of a plant stand and the associated plant responses to local conditions, as well as in simulating the effects of specific plant traits, management choices that influence plant architecture and lighting regimes such as those in greenhouses. For such purposes, functional–structural plant (FSP) models have been developed, which simulate individual plants that interact with each other in 3D, with the changes in plant architecture feeding back on the distribution of environmental drivers that make them grow and develop (light, water, nutrients). In this chapter, the authors outline the purposes of FSP models, the components they need to have in order to serve the purposes mentioned above and give an account of recent applications of such models.