This paper presents DFIT, an R package that implements the differential functioning of items and tests framework as well as the Monte Carlo item parameter replication approach for producing cut-off points for differential item functioning indices. Furthermore, it illustrates how to use the package to calculate power for the NCDIF index, both post hoc, as has regularly been the case in differential item functioning empirical and simulation studies, as well as a priori given certain item parameters. The version reviewed here implements all DFIT indices and Raju's area measures for tests comprised of items modeled with the same parametric item response unidimensional model (1-, 2-, and 3-parameters, generalized partial credit model or graded response model), the Mantel-Haenszel statistic with an underlying dichotomous item response model, and the item parameter replication method for any of the estimated indices with dichotomous item response models.