The four essays published here provide a useful overview for anyone interested in understanding the issues and policy environment surrounding financial system stability. The first three essays consider different aspects of the question, What is financial stability/instability? The first essay, by John Chant, Special Adviser at the Bank in 2001–02, considers how financial instability differs from other kinds of instability, how it is different from the volatility normally associated with a well-functioning financial system, and how instability can be propagated within the financial system and to the real economy. In the second essay, Alexandra Lai tackles some of the problems raised by Chant; in particular, the difficulty of understanding the nature of crises. She reviews a range of theoretical approaches that have been pursued in order to understand the potential instabilities in domestic financial systems. In his essay, Mark Illing provides four case studies of episodes often thought of as periods of financial stress or crisis—the stock market crash of October 1987, the near-collapse of Long-Term Capital Management in 1998, the failures of the Canadian Commercial Bank and the Northland Bank in 1985, and the Bank of New York’s 1985 computer problem. The fourth essay, by Fred Daniel, provides a context for more general discussions of the role of policy in promoting financial stability, by providing an overview of the current institutional arrangements that condition financial behaviour in Canada and how the Bank of Canada interacts with other agencies who share responsibility for financial stability.