The Mass Univariate ERP Toolbox is a freely available set of MATLAB functions for performing mass univariate analyses of event-related potentials (ERPs), a noninvasive measure of neural activity popular in cognitive neuroscience. A mass univariate analysis is the analysis of a massive number of simultaneously measured dependent variables via the performance of univariate hypothesis tests (e.g., t-tests). Savvy corrections for multiple comparisons are applied to make spurious findings unlikely while still retaining a useful degree of statistical power. The advantages of mass univariate analyses include: reduced need for a priori defined time windows/regions of interest, discovery of unexpected effects even when a priori time windows/regions of interest are available, and greater spatial and temporal resolution than conventional mean time window analyses.