This book studies the effect of background knowledge on reading comprehension and investigates the claim from the field of English for Specific Purposes (ESP) that tertiary level students for whom English is a second language should be given reading proficiency tests in their own academic subject areas. The volume includes a comprehensive overview of recent research into reading, in both a first and second language, an account of the development of the reading subtests for IELTS, a full description of the pilot and main phases of the empirical study, a discussion of the relative importance of language proficiency and background knowledge in reading comprehension, consideration of the study's implications for future test construction and research into reading.