Item response theory (IRT) has become one of the most popular scoring frameworks for measurement data. IRT models are used frequently in computerized adaptive testing, cognitively diagnostic assessment, and test equating. This article reviews two of the most popular software packages for IRT model estimation, BILOG-MG (Zimowski, Muraki, Mislevy, & Bock, 1996) and MULTILOG (Thissen, 1991), which are for the first time available on a single CD-ROM with new features. Most prominently, the number of items to be calibrated and examinees to be scored is now limited only by memory capacities of the hardware, MULTILOG has an interactive Windows-oriented process for creating basic command file syntax, and both BILOG-MG and MULTILOG come with a new graphics interface that displays numerous curves relevant to IRT analyses in a professional format. This article reviews the models that are and are not estimable with these programs and describes the fundamental ideas of the underlying estimation algorithms without providing detailed derivations. Moreover, the user-friendliness of both programs is assessed with a user in mind who is interested in easy-to-use IRT estimation programs within a Windows point-and-click environment. Both programs fulfill such an expectation to a large degree; yet, this review also points out some obstacles that someone relatively unfamiliar to IRT or syntax programming might have to overcome to obtain meaningful results.