The aim of this edited book is twofold. First, it provides readers with a deeper understanding of validity, validity evidence and arguments, and the validation process; differing approaches to the validation process; and authentic examples of ways to convey validation arguments for assessments. The book also includes chapters addressing a variety of established and budding areas within assessment and evaluation in mathematics education contexts. Thus, its audience is intended to include anyone who conducts assessment and measurement work in mathematics education contexts.