In this article, I introduce the uirt command, which allows one to estimate parameters of a variety of unidimensional item response theory models (two-parameter logistic model, three-parameter logistic model, graded response model, partial credit model, and generalized partial credit model). uirt has extended item-fit analysis capabilities, features multigroup modeling, allows testing for differential item functioning, and provides tools for generating plausible values with a latent regression conditioning model. I provide examples to illustrate cases where uirt can be especially useful in conducting analyses within the item response theory approach.