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The Houston Myopia Control Study is a 3-year randomized clinical trial in which each of 213 myopic children was placed in either a single vision (standard treatment) group, a +1.00 D add treatment group, or a +2.00 D add treatment group, on the basis of a randomized procedure. Subjects for the three treatment groups were matched on the basis of sex, age, and the initial amount of myopia. The study involves two groups of investigators: an evaluation team, whose task has been to evaluate candidates before entering the study and to reevaluate each subject on a yearly basis for the 3-year period, and a patient care team, whose task has been to prescribe glasses for each subject as well as to counsel subjects and their parents in the correct use of the glasses and to provide a follow-up examination every six months for the duration of the study. Once the glasses had been prescribed, members of the evaluation team were not permitted to know which subjects wore single vision lenses and which wore bifocals. In the interest of good patient care, members of the patient care team knew which subjects wore single vision lenses and which wore +1.00 D add or +2.00 D add bifocals. In this report, the authors discuss theories concerning the etiology of myopia, methods that have been used in an attempt to control the progression of myopia, and the design of the current study. Further reports will present the results of the study on the basis of the data collected by each of the two study teams.