Abstract: This dissertation consists of three independent investigations of interactions between persons and items associated with cultural differences in international assessments of educational achievement. It uses some modified item response models to account for influential elements that are valued differently among nations. The research tackles three specific issues: (1) whether using the measurement unit (imperial versus metric) in the mathematics assessment has an impact on American students' performances; (2) is the tendency to guess in the assessments that adopt the multiple-choice item format constant across nations; and (3) how to make substantive interpretations of the items that exhibit differential item functioning (DIF). Each investigation has its own emphasis varying from test design to model comparison. Together they use a wide range of international assessment data including data for selected countries from the Third International Mathematics and Science Study (TIMSS) and Program for International Student Assessment (PISA). The research also employs a variety of computer programs, i.e., ConQuest, WinBUGS, and the NLMIXED procedure of SAS, all the programs have the flexibility of customizing the item response models for many test situations. All three studies indicate that interactions between the examinees and items may vary systematically from country to country, and item response models need to be carefully selected for the purpose of comparison in the international assessments.