This paper reviews the basic elements of the EM approach to estimating item parameters and illustrates its use with one simulated and one real data set. In order to illustrate the use of the BILOG computer program, runs for 1-, 2-, and 3-parameter models are presented for the two sets of data. First is a set of responses from 1,000 persons to five items of the Law School Admissions Test. Second is a set of simulated data of 1,000 persons to 18 items. The examples bring into focus the degree to which item parameters in the 3-parameter model can be recovered. The review discusses an EM Algorithm for estimating item parameters; solution for item parameters when person ability values are known; early computer program approaches; and the key elements of the Bock-Aitkin approach. Further described are extensions of the Bock-Aitkin approach, which include: (1) extension of the 3-parameter model; (2) prior distributions on item parameters; (3) estimation of the latent distribution; and, (4) different patterns of item attempts for different persons. (PN)