Mastery learning research focuses on learner-oriented and instruction-based factors that relate the concepts of time as a variable and high student achievement as a constant. This research emphasis encompasses optimistic assumptions about the capability of students to learn if: (1) alterable variables are optimized, and (2) diagnostic-instructional procedures based on a medical model of diagnostic-prescriptive interventions are used. Over the past 25 years, mastery learning research has gradually assumed an international character as evidenced by the professional literature. This proliferation, however, has occurred without a concerted effort to accommodate the special features of psychological and educational research in an international context. This paper addresses methodological issues that are initially problematic, yet potentially promising where mastery learning research in the international arena is concerned. Attention is given to such areas as: (1) cross culturalism spanning comparative education and international psychology; (2) multidisciplinary emphases; (3) international databases and resource personnel networks; and (4) a taxonomy of geographic and thematic progressions worldwide. (Contains 142 references.) (Author/SLD)