Book excerpt: Language learning research aims to describe and fully explain how and why language learning takes place, but can fall short of its stated purpose. Systematic, rigorous research is needed if the growing field of language learning is to progress methodically. This book demonstrates and fully explains such a methodology. Given that research in language acquisition yields practical pedagogical implications, it is crucial that it is rigorous and accurate. This book offers a quantitative research methodology that relies on statistical analysis in order to make inferences and conclusions about language learning. Experimental research aims to understand differences between or within groups of learners under manipulated environments. It requires strict control of conditions, enabling interpretations with a low factor of error. Aek Phakiti provides step-by-step guidelines and underlying principles, epistemology and methodology, in a book that is essential for advanced students of language acquisition and language and education.