The growing fields of language acquisition and processing have made great strides in understanding how individuals learn and use more than one language across various stages of life in diverse contexts. This is partly due to the methodological innovations that have been developed and refined in recent years. This volume discusses methodologies used in first, second, and bi/multilingual language acquisition and processing, with practical guidance on how to employ the different methodologies and accompanying possible statistical analyses. The chapters in this volume deal with the ever-changing field of language acquisition and processing as examined by an array of offline behavioural measures, online reaction methods, and physiological measures. This volume focuses on connecting the practical elements of key methodologies to the theoretical questions they are used to answer, guiding the reader through best practices in examining different linguistic questions.