In this book, the authors analyze and compare the ways in which fluency, accuracy and grammatical complexity have been measured in studies of language development in second language writing. More than 100 developmental measures are examined, with detailed comparisons of the results across the studies that have used each measure. The authors discuss the theoretical foundations for each type of developmental measure, and they consider the relationship between developmental measures and various types of proficiency measures. The authors also examine criteria for determining which developmental measures are the most successful, and they suggest which measures are the most promising for continuing work on language development.