WAVETRAIN is a free, open-source software package for investigating periodic travelling wave solutions of partial differential equations. Typically such equations will contain a number of parameters. WAVETRAIN requires that one of these be selected; this parameter is referred to as the control parameter. Focussing on periodic travelling waves introduces an additional parameter, the wave speed. The basic task performed by WAVETRAIN is the calculation of the region of the control parameter - wave speed plane in which periodic travelling waves exist, and additionally where they are stable. WAVETRAIN’s calculations all use the method of numerical continuation. WAVETRAIN is intended to be easy to use, even for users with limited mathematical/computational background. In particular, the input files for WAVETRAIN are all simple text files: users are not required to write any computer programs, and do not need expertise in any programming language or other software. WAVETRAIN includes a plotter to visualise the results of its calculations. WAVETRAIN plots are publication-quality, and can be fine-tuned by the user if required. WAVETRAIN also provides detailed output data files that are accessible to the user if required, and that have an easily comprehensible format.