This chapter covers the methods and measures used in the ERA study, with a special focus on age 15 outcomes. First, the authors outline the sample participation rate for the 15-year follow-up--the percentages in all cases referring to the numbers at the time of initial sample contact. They then describe the measures used in this monograph, starting with those obtained at first contact with respect to functioning at the time of leaving institutional care. Because the group definitions relevant to the follow-up at age 15 are based on assessments at 6 and 11 years of age, they deal with the measures in those assessments first. At 11 years of age, they used a range of specific cognitive tests that might be of predictive value and those are detailed next. Then they discuss measures employed at the 15-year follow-up and those relevant to possible autism as used by Rutter in the separate assessment at 18-20 years. (Contains 10 tables.)