Research into complexity, accuracy and fluency (CAF) as basic dimensions of second language performance, proficiency and development has received increased attention in SLA. However, the larger picture in this field of research is often obscured by the breadth of scope, multiple objectives and lack of clarity as to how complexity, accuracy and fluency should be defined, operationalized and measured. The present volume showcases current research on CAF by bringing together eleven contributions from renowned international researchers in the field. These contributions not only add to the body of empirical knowledge about L2 use and L2 development by bringing new research findings to light but they also address fundamental theoretical and methodological issues by responding to questions about the nature, manifestation, development and assessment of CAF as multifaceted constructs. Collectively, the chapters in this book illustrate the converging and sometimes diverging approaches that different disciplines bring to CAF research. Following the Notes on contributors, chapters in this volume include: (1) Complexity, accuracy and fluency: Definitions, measurement and research (Alex Housen, Folkert Kuiken and Ineke Vedder); (2) Defining and operationalising L2 complexity (Bram Bulte and Alex Housen); (3) Complexity, accuracy and fluency from the perspective of psycholinguistic second language acquisition research (Richard J. Towell); (4) Complexity, accuracy and fluency: The role played by formulaic sequences in early interlanguage development (Florence Myles); (5) The growth of complexity and accuracy in L2 French: Past observations and recent applications of developmental stages (Malin Agren, Jonas Granfeldt and Suzanne Schlyter); (6) The effect of task complexity on functional adequacy, fluency and lexical diversity in speaking performances of native and non-native speakers (Nivja de Jong, Margarita P. Steinel, Arjen F. Florijn, Rob Schoonen and Jan H. Hulstijn); (7) Syntactic complexity, lexical variation and accuracy as a function of task complexity and proficiency level in L2 writing and speaking (Folkert Kuiken and Ineke Vedder); (8) The effects of cognitive task complexity on L2 oral production (Mayya Levkina and Roger Gilabert); (9) Complexity, accuracy, fluency and lexis in task-based performance: A synthesis of the Ealing research (Peter Skehan and Pauline Foster); (10) Measuring and perceiving changes in oral complexity, accuracy and fluency: Examining instructed learners' short-term gains (Alan Paul Tonkyn); (11) The development of complexity, accuracy and fluency in the written production of L2 French (Cecilia Gunnarsson); and (12) A longitudinal study of complexity, accuracy and fluency variation in second language development (Stefania Ferraris). Epilogue (Alex Housen, Folkert Kuiken and Ineke Vedder) and Index are also included. Individual chapters contain references.