We document that the global scope and depth of the crisis the began with the collapse of the subprime mortgage market in the summer of 2007 is unprecedented in the post World War II era and, as such, the most relevant comparison benchmark is the Great Depression (or the Great Contraction, as dubbed by Friedman and Schwartz, 1963) of the 1930s. Some of the similarities between these two global episodes are examined but the analysis of the aftermath of severe financial crises is extended to also include the most severe post-WWII crises as well. As to the causes of these great crises, we focus on those factors that are common across time and geography. We discriminate between root causes of the crises, recurring crises symptoms, and common features (such as misguided financial regulation or inadequate supervision) which serve as amplifiers of the boom-bust cycle. There are recurring temporal patterns in the boom-bust cycle and their broad sequencing is analyzed.