This book investigates the influence of test taker characteristics on performance in tests of English as a foreign language by exploring the relationships between these two groups of variables. Data from a test taker questionnaire and performance on the First Certificate in English (FCE) and the Test of English as a Foreign Language (TOEFL) were used for the study. The research was conducted in a construct validation context and aimed to increase our understanding of the individual differences among test takers that influence their test performance. The application of a structural modeling approach to investigate the influence of test taker characteristics on test performance makes this study a valuable contribution to language testing research. As such, it will be of considerable relevance to academic researchers and graduate students in the field of language testing and assessment, as well as to others interested in second language acquisition and learning.