This report shows a classification of differential item functioning (DIF) sources that have an effect on the adaptation of tests. This classification is based on linguistic and cultural criteria. Four general DIF sources are distinguished: cultural relevance, translation problems, morph syntactical differences, and semantic differences. The influence of these on the adaptation of tests is greater among those languages belonging to different linguistic families as the cultural distance among the groups increases. The model offered is contrasted empirically through the analysis of 53 verbal items from a Spanish reference sample and a Basque focal sample. The DIF is aided by the Mantel-Haenszel procedure. In addition, a group of experts cataloged each of the items in terms of the DIF sources defined by the model. The level of agreement between the two procedures, judgmental and statistical, stands at 69.8%.