This volume explores the potential of using both cross-sectional and longitudinal learner corpora to investigate the interlanguage of learners with various L1 backgrounds and to subsequently apply the findings to language teaching and assessment. It is made up of 18 chapters selected from papers presented at the international conference «Compiling and Using Learner Corpora», held in May 2013 at the University of Padua, Italy. The chapters discuss current issues and future developments of the use of learner corpora, present case studies based on teaching and assessment experiences in various contexts, and longitudinal corpus-based studies conducted within the Longitudinal Database of Learner English (LONGDALE) project. Other chapters report on investigations of specific aspects of the interlanguage of a variety of learner populations, and the last ones address issues of corpus compilation and representativeness. The majority of the contributions draw on data produced by EFL learners from Germany, Italy, Japan, Spain, and the Netherlands, while others concern learners of Italian and Spanish as Foreign Languages.