This state-of-the-art article describes two types of verbal-report data (i.e., concurrent and retrospective) and four major introspective methods used in second language (L2) research (i.e., thinking-aloud, questionnaires, interviews, and diary-keeping). It then summarizes major introspective L2 research conducted to date, followed by a methodological review from ten perspectives which serve as criteria for classifying and evaluating these introspective L2 studies. It concludes with a discussion of presently controversial issues amongst researchers over the use of introspection as a research method for tapping L2 learners' inner cognitive processes, suggesting ways of minimizing concerns raised about verbal reports. It is argued that although verbal reports from informant-learners may be an incomplete reflection of actual internal processing, and enough care must always be exercised in stages of data collection and interpretation, they nevertheless contain useful information concerning learners' mental processes including their use of learning strategies which will not be satisfactorily accessed through extrospective observational studies.