Second language (L2) computer-adaptive testing (CAT) is a technologically advanced method of assessment in which the computer selects and presents test items to examinees according to the estimated level of the examinee's language ability. The basic notion of an adaptive test is to mimic automatically what a wise examiner would normally do. Specifically, if an examiner asked a question that turned out to be too difficult for the examinee, the next question asked would be considerably easier. This approach stems from the realization that little is learned about an individual's ability if the questions posed are far too difficult or far too easy for that person. This digest discusses the following issues related to computer adaptive testing: (1) advantages of using computer-adaptive testing in second language assessment; (2) roots and challenges of computer-adaptive testing; (3) issues involving the basic principles of assessment in computer-adaptive testing; (4) CAT and the basic principles of test reliability; (5) CAT and the basic principles of test validity; and (6) CAT item pools for measuring the identified ability of the examinee population. (Contains 9 references.) (VWL)