Terrestrial ecosystems undergo temporal dynamics in plant populations, community composition, and ecosystem structure. These changes in ecosystems are driven by demographic processes of recruitment, establishment, growth, and mortality and require models distinctly different from biogeochemical models. This chapter provides an overview of this class of models with three specific examples. Individual-based forest gap models track the birth, growth, and death of individual trees in an area of land. Dynamic global vegetation models simulate changes in the area occupied by discrete patches of plant functional types. Ecosystem demography models define patches based on age since disturbance and simulate the dynamics of cohorts of similar plant functional types rather than tracking every individual. Common to each model is the representation of vegetation demography, with age- and size-dependent growth and mortality and in which growth is constrained by allometric relationships of stem diameter with height, sapwood area, leaf area, and biomass. Rather than biogeochemical cycles, vegetation demography provides the dynamical core for the next generation of terrestrial biosphere models.