This investigation of the comparability of writing assessment prompts was conducted in two phases. In an exploratory Phase I, 47 writing prompts administered in the computer-based Test of English as a Foreign Language™ (TOEFL CBT) from July through December 1998 were examined. Logistic regression procedures were used to estimate prompt difficulty and gender effects. A panel of experts reviewed selected prompts, and a taxonomy of prompt characteristics was developed and related to prompt difficulty and gender differences. In Phase II, 87 prompts administered from July 1998 through March 2000 were analyzed. All of the prompts used in Phase I, together with 40 new prompts, were analyzed using the larger Phase II database.Recommendations are made for statistical quality control procedures to identify less comparable prompts.Key words: computer-based writing assessment, essay prompts, comparability, fairness, polytomous DIF (differential item functioning), gender, logistic regression, proportional odds-The Test of English as a Foreign Language™ (TOEFL ® ) was developed in 1963 by the National Council on the Testing of English as a Foreign Language. The Council was formed through the cooperative effort of more than 30 public and private organizations concerned with testing the English proficiency of nonnative speakers of the language applying for admission to institutions in the United States. In 1965, Educational Testing Service ® (ETS ® ) and the College Board ® assumed joint responsibility for the program. In 1973, a cooperative arrangement for the operation of the program was entered into by ETS, the College Board, and the Graduate Record Examinations (GRE ® ) Board. The membership of the College Board is composed of schools, colleges, school systems, and educational associations; GRE Board members are associated with graduate education.ETS administers the TOEFL program under the general direction of a policy board that was established by, and is affiliated with, the sponsoring organizations. Members of the TOEFL Board (previously the Policy Council) represent the College Board, the GRE Board, and such institutions and agencies as graduate schools of business, junior and community colleges, nonprofit educational exchange agencies, and agencies of the United States government.A continuing program of research related to the TOEFL test is carried out under the direction of the TOEFL Committee of Examiners. Its 12 members include representatives of the TOEFL Board and distinguished English as a second language specialists from the academic community. The Committee meets twice yearly to review and approve proposals for test-related research and to set guidelines for the entire scope of the TOEFL research program. Members of the Committee of Examiners serve four-year terms at the invitation of the Board; the chair of the committee serves on the Board.Because the studies are specific to the TOEFL test and the testing program, most of the actual research is conducted by ETS staff rather than by outside researche...