This book focuses on assessing L2 student digital multimodal composing (DMC) competence. It explores key themes, including the conceptualization of L2 student DMC competence, and the development, validation, and utilization of L2 student DMC competence in the tertiary context.Through a thorough review of the DMC literature, the book furnishes readers with a theoretical framework to comprehensively grasp the underlying constructs of L2 student DMC competence. It also provides a delineation of the process of scale development, i.e., defining constructs, constructing items, and analyzing items, scale validation, i.e., the structural, external, and consequential construct validity of the scale, and scale utilization in students' DMC self- and peer-assessment practices.This practical guidance equips educators and practitioners with the necessary tools and strategies to effectively assess and enhance L2 students' DMC competence. Scholars and professionals in the fields of L2 writing, language assessment, digital literacy, and technology-enhanced language learning will gain valuable insights from the content.