The logic and uses of test equating are discussed, including three methods of test equating. The focus is on the conceptual underpinnings of each test equating method, rather than on the mathematics of the procedures. Additional consideration is given to the assumptions of each method and its respective strengths and weaknesses. A commonly accepted definition of equivalent scores is based on the concept of equipercentile equating. The first step is to determine the percentile ranks of the distribution of scores on both instruments. The percentile ranks are then plotted against the raw scores for each instrument, and once they are graphed, equivalent scores can be obtained from the graph. The linear equating method is based on the assumption that the two forms of the test, which are designed to be parallel, will have essentially the same raw-score distributions, apart from minor differences in the mean and standard deviations. Item response theory (IRT), or latent trait theory, is an attempt to measure a person's performance on a test item as a function of the difficulty of the item and the examinee's performance on some unobserved, or latent, trait. The three IRT models are discussed, and conditions under which all equating methods are similar are reviewed. (Contains 1 table, 2 figures, and 18 references.) (Author/SLD)