Asset Price Bubbles (Volumes 1 and 2) are based on the two mechanisms used to characterize security prices in markets: no arbitrage (Volume 1) and equilibrium (Volume 2). No arbitrage is the weaker of the two assumptions, being implied by an equilibrium. Being a weaker assumption, it applies in more market settings. However, because it is a weaker assumption, less can be said about the impact of price bubbles on trader behavior and the macro-economy. No arbitrage is the mechanism emphasized in Volume 1. Issues related to trader behavior, equilibrium, and the macro-economy, including the impact of bubbles on financial stability are contained in Volume 2.