Recent episodes of financial turmoil, and especially the global financial crisis of 2007-2008 and its aftermath, underscore the need to understand better the forces behind asset bubbles and crashes. What are their root causes – investor irrationality, excessive risk-taking, misguided policies? And what explains the magnitude of their effects – including the contagion across assets, investors, and countries? How should policy makers balance the dual risks of the post-crisis world -- growth stagnation, on the one hand, and recurrent asset bubbles and crashes, on the other? This seminar will summarize current thinking on bubbles and crashes, and the policy challenges they pose in a financially-globalized world.