The present study investigates the nature of communicative language ability as manifested in performance on the TOEFL iBT® test, as well as the relationship between this ability with test-takers' study-abroad and learning experiences. The research interest in the nature of language ability is shared by the language testing community, whereas understanding the factors that affect language acquisition has been a focus of attention in the field of second language acquisition (Bachman & Cohen, 1998). This study utilizes a structural equation modeling approach, a hybrid of factor analysis and path analysis, to address issues at the interface between language testing and second language acquisition. The purpose of this study is two-fold. The first has a linguistic focus: to provide empirical evidence to enhance our understanding of the nature of communicative language ability by examining the dimensionality of this construct in both its absolute and relative senses. The second purpose, which has a social and cultural orientation, is to investigate the possible educational, social, and cultural influences on the acquisition of English as a foreign language, and the relationships between test performance and test-taker characteristics. The results revealed that the ability measured by the test was predominantly skill-oriented. The role of the context of language use in defining communicative language ability could not be confirmed due to a lack of empirical evidence. As elicited by the test, this ability was found to have equivalent underlying representations in two groups of test-takers with different context-of-learning experiences. The common belief in the superiority of the study-abroad environment over learning in the home country could not be upheld. Furthermore, both study-abroad and home-country learning were proved to have significant associations with aspects of the language ability, although the results also suggested that variables other than the ones specified in the models may have had an impact on the development of the ability being investigated. From a test validation point of view, the results of this study provide crucial validity evidence regarding the test's internal structure, this structure's generalizability across subgroups of test-takers, as well as its external relationships with relevant test-taker characteristics. Such a validity inquiry contributes to our understanding of what constitutes the test construct, and how this construct interacts with the individual and socio-cultural variables of foreign language learners and test-takers.