Mutational processes leave characteristic footprints in genomic DNA. The MutationalPatterns R package provides an easy-to-use toolset for the characterization and visualization of mutational patterns in base substitution catalogues of e.g. tumour samples or DNA-repair deficient cells. The package covers a wide range of patterns including: mutational signatures, transcriptional strand bias, genomic distribution and association with genomic features, which are collectively meaningful for studying the activity of mutational processes. The package provides functionalities for both extracting mutational signatures de novo and inferring the contribution of previously identified mutational signatures in a given sample. MutationalPatterns integrates with common R genomic analysis workflows and allows easy association with (publicly available) annotation data. Availability and implementation: The MutationalPatterns R package is freely available for download at https://github.com/CuppenResearch/MutationalPatterns. The package documentation provides a detailed description of typical analysis workflows.