This book presents research on the development of tasks for teaching and assessing English proficiency at different CEFR-J levels across the five language skills: listening, reading, spoken interaction, spoken production, and writing. Based on research on CEFR-J, an English proficiency framework developed for Japanese learners of English, the book provides a detailed account of the process from the analysis and interpretation of can-do descriptors to the design of task themes, selection of materials, development of test items, and construction of assessment methods.