This book derives from a study which explores the impact of students interactions and knowledge construction on ESL (English as a Second Language) writing Performance. The primary focus of the study centers on how participants communicate via email in a collaborative learning environment incorporating process writing approach and pair work activity. The study addresses these concerns by investigating three main areas; interactions, knowledge construction process and writing performance. In addition, this study employs online interviews to elicit participants' perceptions and as supplementary information on the efficacy of email discussion.