In Volume 5 of the Annual Review of Financial Economics, we continue focusing on the role of banks and credit in the recent financial crisis with articles on too big to fail, credit-rating agencies, corporate governance for banks, bank leverage and real interest rates, and financial contagion in...

We examine the implications of portfolio theory for the cross-sectional behavior of equity trading volume. Two-fund separation theorems suggest a natural definition for trading activity: share turnover. If two-fund separation holds, share turnover must be identical for all securities. If...