Codes used to simulate aerosol behavior inside containments of nuclear power plants after assumed severe accidents are described. The basic aerosol physical equations of all codes are the same worldwide. Only minor differences can be detected regarding some special aerosol physical processes. These differences are not inherent but caused by boundary conditions, which are of special interest for the code users. The comparison of the single codes also shows that the general agreement achieved by the numerical treatment of the aerosol equation requires an appropriate discretization of the distribution function to yield stable solutions under all arbitrary conditions. The application of solutions based on special distribution functions should, therefore, be restricted to certain scenarios.