A replication study repeats, exactly or approximately, a previous study to discover if its findings are reliable and/or can be generalised to other participants and circumstances. It is accepted practice in many disciplines that quantitative research studies can be replicated to have their robustness and generalisability tested. This edited volume brings together a number of experts who argue in favour of a more central role for replication research in Second Language Acquisition and Applied Linguistics. The book provides a theoretical argument to support this view, as well as practical examples and model replication studies. It includes practical advice on how best to carry out replication research, covering issues such as how to choose suitable studies to replicate and how to set up, execute and write up the research ready for presentation to a journal.