IRS Office of Research Headquarters measures and models taxpayer burden, defined as expenditures of time and money by taxpayers to comply with the federal tax system. In this research activity, IRS created two microsimulation models using econometric techniques to enable the Service to produce annual estimates of taxpayer compliance burden for individual and small business populations. Additionally, a Discrete Event Simulation (DES) model was developed to represent taxpayer activities and IRS administration in postfiling processes. This paper discusses the development of the DES Postfiling Model and compares microsimulation and DES approaches from the perspectives of policy measurement, flexibility and reporting by IRS analysts. The main strengths of microsimulation are robust segmentation of results and the ability to support representation of imbedded, joint distributions in a complex, structural model. The strengths of using DES are its queuing capability and increased flexibility to update the granularity of both the data and process changes.