This article discusses the judicial review of legislation. Judicial review of legislation is now a well-established practice in most constitutional democracies. Many of the theoretical issues have been fully explored, primarily in the literature emerging from the United States, where the practice has been in place the longest. New forms of judicial review, and new constitutional commitments to social welfare rights, raise important empirical questions about the performance of courts and legislatures. The largest gains in scholarly understanding to be made in the next decade are likely to come not from further theoretical explorations but from empirical inquiries into the actual operation of various systems of judicial review, with respect to a range of constitutional issues.