Internationalization International students Adaptation Higher education Scale developmentEmbracing a holistic and eclectic perspective, this study aims to develop and empirically test an instrument to assess international students' general adaptation to a host country. The data were obtained from a sample of international undergraduate students (n=843) studying at a Turkish state university using purposive sampling methods of maximum variation. The analyses were conducted in two consecutive phases with two different groups of international students. Upon a meticulous data clean-up and preliminary analyses for the assumptions of normality and reliability, exploratory factor analysis (EFA) to discover factor structure was utilized. In the second phase, confirmatory factor analysis (CFA) was performed through Lisrel to validate the scale structure revealed by EFA. After a rigorous and iterative scale development process, the results confirm the reliability of factors, model fit and construct validity of the General Adaptation Scale for International Students (GASIS). GASIS as a multi-dimensional instrument consists of 28 items using a five-point Likert scale with four factors labelled as academic adaptation, sociocultural adaptation, psychological adaptation, and daily life adaptation to assess international students'general adaptation levels. The final form of 28-item GASIS with psychometric features, as well as implications and limitations for future research are included in the study.