R package DSsim. Performs distance sampling simulations. It repeatedly generates instances of a user defined population within a given survey region, generates realisations of a survey design (currently these must be generated using Distance software in advance <http://distancesampling.org/>) and simulates the detection process. The data are then analysed so that the results can be compared for accuracy and precision across all replications. This will allow users to select survey designs which will give them the best accuracy and precision given their expectations about population distribution. Any uncertainty in population distribution or population parameters can be included by running the different survey designs for a number of different population descriptions. An example simulation can be found in the help file for make.simulation.