Most molecular simulations use 2-body (1/r^6) van der Waals (VDW) interactions between atoms and molecules. Only occasionally are 3-body calculations included in the simulations. Here we show the "coupled dipole method", which is used to calculate all n-body interactions between atoms and molecules in an exact way. The model is able to account for any placement of atoms or molecules. The data required for our model are Drude parameters (alpha0 and freq0). We demonstrate cases where our results give the same VDW forces as Lifshitz theory, and then show examples where significant differences are obtained between 2-body calculations and n-body calculations, such as surface tensions and nanoscale systems. This talk describes the physics and algorithm of the coupled-dipole method and gives a number of demonstrative calculations.