This edited book is a collection of papers, written by language assessment professionals to reflect the guidance of Professor Lyle F. Bachman, one of the leading second language assessment experts in the field for decades. It has three sub-themes: assessment of evolving language ability constructs, validity and validation of language assessments, and understanding internal structures of language assessments. It provides theoretical guidelines for practical language assessment challenges. Chapters are written by language assessment researchers who graduated from the University of California, Los Angeles, where Professor Bachman trained them including the book editors.