Abstract--Validation in language testing requires test designers to make an argument for the validity of inferences from and uses of test scores. Development of such an argument draws upon theoretical rationales and empirical evidence that have their basis in test design. Despite the advances in second language testing over the past two decades, fundamental limitations remain in the design of language tests'limitations linked to the manner in which test developers conceptualize and analyze language. Based on test design projects that I have worked on, this paper demonstrates the need for engagement with linguistics to address lingering problems in test design. One problem all language test designers face is how they can best conceptualize the construct of language ability that a particular test is intended to measure, particularly in view of the role of the context of situation in all language performance. A second problem in test design is how to identify the language in a text that poses particular comprehension difficulty to readers or listeners. A third problem is the need for well-motivated frameworks for designing tests that are sensitive to the linguistic development of second language learners. The paper will illustrate each problem from testing projects and point to advances relevant to validation that may be possible if test designers could draw upon a more sophisticated understanding of linguistics. Carol Chapelle is Professor of TESL/applied linguistics and Chair of Linguistics at Iowa State University. She is Vice-President of the American Association for Applied Linguistics. Her research explores issues at the intersection of computer technology and applied linguistics. Recent books are "Computer applications in second language acquisition: Foundations for teaching, testing, and research" (Cambridge University Press, 2001) and "English language learning and technology: Lectures on applied linguistics in the age of information and communication technology" (John Benjamins, 2003). Forthcoming books focus on language assessment: "Assessing language through technology" (Chapelle & Douglas; Cambridge University Press, forthcoming) and "ESOL tests and testing: A resource for teachers and administrators" (Stoynoff & Chapelle; TESOL Publications, 2005). She is a former editor of TESOL Quarterly (1999-2004), and her papers have appeared in journals such as TESOL Quarterly, Language Learning, Language Testing, and Language Learning & Technology. She teaches courses in applied linguistics at Iowa State University and has taught in Arizona, Hawai'i, Michigan, Spain, and Canada. She has lectured at conferences in Chile, Denmark, England, France, Japan, Morocco, Scotland, Singapore, South Korea, Spain, and Taiwan.