It has long been noted that high-stakes language exams exert a powerful influence on teaching and learning, a phenomenon known as the "washback effect "(Alderson and Wall, 1993). However, due to the complex nature of the phenomenon, little research has been conducted in the field so far. This book, which is based on empirical research into the "washback effect" of First Certificate in English (FCE, Cambridge ESOL), discusses and elaborates on the complexity of the phenomenon and accounts for the intervening factors that mediate the process of test washback. The book concludes with the presentation of a model that demonstrates how the mechanism of washback operates and with recommendations to a variety of stakeholders for achieving beneficial washback.