The concept of validity, which concerns the truth-value of a test and its scores, is both powerful and precarious: powerful because it dominates all aspects of language testing; and precarious because it responds uneasily to four challenges. These are first, the challenge of the appeal to logic and to syllogistic reasoning; second, the challenge of the claims of reliability; third, the challenge of the local and the universal; and fourth, the challenge of the unitary and the divisible. In this chapter we will first discuss the concept of validity, making use of these three causes of concern; we will then takeup the issueofvalidationandexaminewith exemplificationhowfardifferent approaches to validation meet the requirements of validity. It is through validation that validity is established, which means that validity is only as good as its validation procedures.