This book clarifies the concept of impact and related terms, such as washback, evaluation, monitoring and validation, and focuses on the impact of language tests and language programmes on a range of stakeholders, including test-takers, teachers, textbook writers, testers and institutions. First-hand experience is cited from two new impact studies. One analyses the impact of the International English Language Testing System (IELTS), the second looks at the Progetto Lingue 2000 (Year 2000 Languages Project), a state-school foreign-language education improvement programme undertaken by the Ministry of Education in Italy. The main findings of these studies are presented, as well as theoretical and practical lessons to be learnt from them. The context is the role of impact studies in the test development and validation systems of Cambridge ESOL, the sponsor of both impact studies.