What is liquidity and why is it so important for firms and financial institutions to command enough liquidity? This book brings together classic articles and recent contributions to this important field of research. It provides comprehensive coverage of the role of liquidity in financial crises and is divided into five parts: (i) liquidity and interbank markets; (ii) the public provision of liquidity and regulation; (iii) money, liquidity, and asset prices; (iv) contagion effects; (v) financial crises and currency crises.