A model for the characterization of in-vitro dissolution profiles is presented. The basis is a mathematical expression designated the Order Model which incorporates four parameters: the kinetic order, a rate constant, a gradual introduced lag-time and the assay level. Data fitting is performed by non-linear regression using standard PC software. It is emphasized that the order need not be an integer which will enhance the applicability of the model. Interpretation and applicability of the model are discussed in relation to different release systems. The cube-root law is a special case of the Order Model with the order = 23. The high degree of fitting possible with the Order Model is illustrated on three products: individual pellets, ensembles of pellets and tableted pellets. Arguments are provided that an increased inhomogeneity of the ensemble of pellets will lead to a higher kinetic order.