IELTS (the International English Language Testing System) and its predecessor ELTS have served for over 25 years as a high-stakes proficiency test to assess the English language skills of international students wishing to study or train in English-speaking environments. During that time the test has been regularly revised in light of findings from ongoing research and validation studies to ensure that it remains a valid and reliable measure. This book brings together a collection of research studies conducted between 1995 and 2001 under the auspices of the British Council/IELTS Australia Joint-funded Research Program which promotes independent research among IELTS stakeholders worldwide. The ten studies - four on speaking and six on writing assessment - provided valuable test validity evidence and directly informed the revised IELTS Speaking and Writing tests introduced in 2001 and 2005.