Identifying the sources of differential item functioning (DIF) in international assessments is very challenging, because such sources are often nebulous and intertwined. Even though researchers frequently focus on test translation and content area, few actually go beyond these factors to investigate other cultural sources of DIF. This article introduces the multiple-variable matching method using logistic regression analysis to identify sources of DIF. A case study demonstrates how this methodology identified Extra Lesson Hours After School (ELHAS) as a potential source of DIF between Taiwan and the United States in the Third International Mathematics and Science Study (TIMSS) 1999. DIF is not a fixed character of any test item, nor is a cultural factor an inherent source of DIF. The legitimacy of a source of DIF relies on the specific context and purpose for the cross-country comparison.