In recent decades, the use of large-scale standardized international assessments has increased drastically as a way to evaluate and compare the quality of education across countries. In order to make valid international comparisons, the primary requirement is to ensure the measurement equivalence between the different language versions of these assessments due to their multilingual and cross-cultural nature. In this study, we investigated the measurement equivalence of one of the most popular international assessments, PISA (Programme for International Student Assessment), between U.S. and Canadian, Hong Kong and mainland Chinese, and U.S. and mainland Chinese students. Both unidimensional and multidimensional random coefficient multinomial logit model (RCML) were applied to detect differential item functioning (DIF). Furthermore, we exerted great efforts to identify possible explanations of DIF via detailed content analyses. The results showed that the number of DIF items is the smallest between Canadian and U.S. students and the largest between U.S. and Chinese students. We also noticed that for all three comparisons the number of DIF items reduced significantly when we analyzed the data using the multidimensional approach. Our content analysis revealed that language difference only accounted for a small proportion of DIF between U.S. and Chinese students, whereas differential curriculum coverage was found to be the most serious cause of DIF in both the Hong Kong-Mainland and the U.S.-Chinese comparisons. In addition, we found that differential content familiarity is also a potential cause of DIF. Further investigations of more potential sources of item bias require the collection of additional data. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]