An elementary survey of item characteristic curve theory, centered around the problems of individualized (tailored) testing, is presented. Following the introduction, discussions are provided of the following: Test Theory for Itemized Tests; The Guttman Scale; Item Characteristic Curve Theory; An Alternative Model; Specialization, Application, and Evaluation; Pretesting; The Statistical Estimation of Ability; A Simpler Procedure for Estimating Ability; Stochastic Approximation; The Staircase Method for Selecting the Test Questions; Scoring the Answers; Evaluation of Testing Methods; and Relation to Psychophysical Methods. An extensive list of references is provided. (DB)