There is some confusion concerning what is meant by a quantitative model. This is caused primarily by the existence of a wide variety of model users. Quantitative models may be purely empirical (based solely on data sets), semiempirical (relying on physics whenever appropriate and available but the ‘gaps’ being filled in with data as necessary), or physical (based on the physics of the processes). Most quantitative modeling efforts at this point in time are semiempirical, which is partly because the physics of the magnetosphere is not yet entirely understood. At the same time, however, there is a large user community that needs models which can accurately describe magnetospheric features. The preponderance of semiempirical models results from the fact that current data sets describing various magnetospheric features and processes are limited.