Many books have been written on the topic of second language assessment, but few are easily accessible for both students and practicing language teachers. This textbook provides an up-to-date and engaging introduction to this topic, using anecdotal and real-world examples to illustrate key concepts and principles. It seamlessly connects qualitative and quantitative approaches and the use of technologies, including generative AI, to language assessment development and analysis for students with little background in these areas. Hands-on activities, exercises, and discussion questions provide opportunities for application and reflection, and the inclusion of additional resources and detailed appendices cements understanding. Ancillary resources are available including datasets and videos for students, PowerPoint teaching slides and a teacher's guide for instructors. Packed with pedagogy, this is an invaluable resource for both first and second language speakers of English, students on applied linguistics or teacher education courses, and practicing teachers of any language.