Causes of the Great Depression
Second, there are the monetarists, who believe that the Great Depression started as an ordinary recession, but that significant policy mistakes by monetary authorities (especially the Federal Reserve) caused a shrinking of the money supply which greatly exacerbated the economic situation, causing a recession to descend into the Great Depression. Related to this explanation are those who point to debt deflation causing those who borrow to owe ever more in real terms.
Great Depression
The causes of the Great Recession seem similar to the Great Depression, but significant differences exist. The previous chairman of the Federal Reserve, Ben Bernanke, had extensively studied the Great Depression as part of his doctoral work at MIT, and implemented policies to manipulate the money supply and interest rates in ways that were not done in the 1930s. Generally speaking, the recovery of the world's financial systems tended to be quicker during the Great Depression of the 1930s as opposed to the late-2000s recession.