To better understand the dissolution of porous media and underground cavities is very important in various applications. In this chapter, pore-scale dissolution model, which involves thermodynamic equilibrium or nonlinear reactive boundary conditions, is upscaled into Darcy-scale using the method of volume averaging. In the Darcy-scale model, several effective parameters are employed to describe the average behaviors of the pore-scale features, and they can be obtained by solving specific closure problems. The developed Darcy-scale model is validated by taking the dissolution of a gypsum pillar as an example. The results show that when Péclet and Reynolds number are within the assumptions to apply volume averaging, computation results using Darcy-scale model agree very well with direct numerical simulations. However, when they go beyond certain limits, 3D effects have to be taken into consideration.