Test developers need to provide a clear explication of the language ability constructs that underpin the tests they offer in the public domain; such an explication is essential for supporting claims about the validity - or usefulness - of test scores. This volume describes the theory and practice of Cambridge ESOL's approach to assessing second language writing ability. A comprehensive test validation framework is used to examine the tasks in Cambridge ESOL writing tests from a number of different validity perspectives that reflect the socio-cognitive nature of any assessment event. The authors show how an understanding and analysis of the framework and its components can assist test developers to operationalise their tests more effectively, especially in relation to the key criteria that differentiate one proficiency level from another. The book provides: an up-to-date review of relevant literature on assessing writing, an accessible and systematic description of the different proficiency levels in second language writing, a comprehensive and coherent basis for validating tests of writing. This volume is a rich source of information on all aspects of examining writing ability. As such, it will be of considerable interest to examination boards who wish to validate their own writing tests in a systematic and coherent manner, as well as to academic researchers and students in the field of language assessment more generally. Book jacket.