In the pharmaceutical literature the dissolution of solids in liquids is usually described using the stagnant layer model. This model, however, does not reflect the actual situation with respect to the hydrodynamics involved. This review analyses the different hydrodynamic situations in which dissolution may take place. It appears that dissolution of regular, non-disintegrating surfaces under forced convection, in laminar as well as in turbulent flow, can be described mathematically. The same holds true for dissolution in a laminar natural convection flow parallel to a vertical dissolving surface. All these situations can be treated using a general expression for the dissolution rate (R) containing five basic parameters,i.e. solubility (Cs), diffusion coefficient (D), kinematic viscosity (v), flow velocity (u) and a geometric factor (A) which is a function of the shape and dimensions of the dissolving surface, thus $$R = KC_S D^\beta {\text{ }}v^\gamma {\text{ }}u^F A$$ The exponentsΒ,γ ande, the proportionality factor K and the geometric factor A, which is defined as A = f (b, l, r, d), depend on the hydrodynamic conditions in each particular case of solvent motion. Most of these values were derived theoretically and confirmed experimentally. In contrast to this it appears to be impossible at present to describe the dissolution process under natural convection conditions if the flow is not parallel to the dissolving surface. In conclusion it is evident that analysing dissolution processes, using hydrodynamic theories, provides a better insight in the process itself and the factors influencing it both qualitatively and quantitatively. Only this will permit correct interpretation of actual dissolution rate data.