This essay explains in very simple words the problems encountered by banks during periods of severe economic crises, like the crises of 1929 and of 2008. Moreover the document describes the means that banks have at their disposal to combat such crises.This is a non technical document and does not assume any prior knowledge on behalf of the reader. A genuine interest will suffice. After reading this essay, the reader will have an understanding of banking crises. What they are and what can be done about them.