In this report, the authors aim to review and advance knowledge of systematic ways of classifying thinking skills. They concentrate on taxonomies and theory-based frameworks, in the belief that studying and using them will promote better understanding of how people think and learn at the age of 16 or above. Their overarching interest is in how that understanding can inform instructional design, course and lesson planning, teaching, learning and assessment. In particular, they aim to identify: key principles on which teaching approaches designed to develop thinking skills depend helpful ways for teachers and learners to classify and talk about thinking skills. The authors believe that further research with, and use of, thinking skill frameworks will lead to a better understanding of how people think and learn. They conclude by making a set of recommendations for policy-makers. Appendices include: (1) Theoretical frameworks for thinking about thinking; (2) Descriptions and evaluative summaries of 26 frameworks; (3) "Reason!Able" evaluations; and (4) Using an integrated framework for understanding thinking and learning to categorise Costa and Kallick's (2000a) "habits of mind". (Contains 13 figures, 50 tables, and 5 footnotes.)