Language researchers and practitioners often adopt tools and techniques without testing whether they really work as they should. This is understandable because most scholars do not have the time or expertise to properly evaluate the usefulness of all instruments, measures, and methods they need. It is therefore critical to have problem solvers in the field who gain the necessary expertise and take the time to scrutinize existing methods, identify problems, and offer new solutions. This volume represents the work of scholars who have done this; it is a collection of the latest advances, developments, and innovations regarding the modeling and measurement of learners’ vocabulary growth curves, current levels of vocabulary knowledge and lexical proficiency, and the patterns of lexical diversity found in their language production. Several of the contributors also address the complex but important relationship between automated indices and human judgments of learners’ lexical patterns and abilities.