This book is the result of our approaches of validation enquiry that were applied on the data obtained from a language proficiency test,conssiting of grammar, vocabulary and reading comprehension carried out with 3,398 PhD candidates as a partial requirement for entering PhD programs in Iran. The four approaches were facotr analysis, multitrait multimethod, test taking strategies and internal correalitons. All approches provided evidnec for the construct validity of the test. The book is replete with valuable information on how to conduct validation studies. Although the study was conduced in an Iranian context, implications are pertinent for international applications