The marked expansion of education at all levels from early childhood education to primary and secondary schooling, as well as to universi¬ties and institutes of technology and to programs of lifelong learning and recurrent education in the workplace, led to the development of educational research as a major field of scholarly inquiry during the second half of the twentieth century. Research into education involves many disciplines in addition to psychology and operates with large numbers of individuals, institutions and systems at several levels across the approximately 200 states of the world. Moreover, it neces¬sarily involves change over time since it is specifically concerned with the learning and development of young people, who are being taught in an increasingly complex world. During the years from 1962 to 1992 the authors of this chapter were actively engaged in the research stud¬ies of the International Association for the Evaluation of Educational Achievement (IEA). IEA formed part of this movement for the advancement of education and educational research. This chapter examines the links between IEA and the developments that occurred in educational research methods and measurement. These links included the conduct of research studies that involved: (a) large num¬bers of students, teachers and schools, (b) methods and procedures for the examination and the analysis of data, (c) the measurement of change over time and across countries, (d) the testing of models and hypotheses for statistical and practical significance, and (e) the draw¬ing of implications from the findings for policy and practice in the field of education.