This book offers a succinct theoretical introduction to the basic concepts in language testing in a way that is easy to understand. In the Japanese context, this book is highly recommended for university faculty members involved in obtaining assessment literacy, teachers who want to validate their exploratory teaching and testing, or applied linguistics students new to the language testing field. The book is divided into four main sections. The first provides an overview of the principles of language testing. The next contains short extracts from the testing literature with questions which stimulate further thinking. Section 3 is a list of references with brief annotations and Section 4 a glossary of referenced testing terms.