Estimation of person parameters (abilities) for the 1, 2, 3 and 4 parameter logistic model, the (generalized) partial credit model and tests that mix dichotomous and polytomous items, under the assumption that the item parameters are known and fixed: maximum likelihood, weighted likelihood (Warm, 1989 <doi:10.1007/BF02294627>), maximum and expected a posteriori and robust estimation (Schuster and Yuan, 2011 <doi:10.3102/1076998610396890>). Further features are jackknife estimates (Wainer and Wright, 1980 <doi:10.1007/BF02293910>), plausible values, the person fit statistics lz, lz* (Snijders, 2001 <doi:10.1007/BF02294437>), infit and outfit, and the simulation of response data. Models fitted with the eRm package can be passed on directly. The package is useful, e.g., when items of an item bank are given to a new sample of persons.