To provide the users of the GROMACS MD package 13 with access to simulations at constant pH, we have implemented the λ-dynamics based constant pH approach by Brooks and co-workers. In contrast to the previous implementation in a fork of GROMACS 3.3, 10 the new implementation, which is described in an accompanying paper, 15 is efficient and constant pH MD simulations can be performed with little computational overhead compared to normal MD simulations. The purpose of this paper is to provide users with guidelines and recommendations on how to set up and perform constant pH MD simulations, including the necessary parameterization steps.