It's fun to talk about what money is, but often it's hard to connect the dots and make it actually relevant to the discussion of the economy and markets. But, in this episode, we do just that. Our guest is Jacob Goldstein, a co-host of Planet Money and the author of the new book, “Money: The True Story Of A Made-Up Thing”. He explains the story of money market mutual funds, how they constituted a new form of money, and how they contributed to the Great Financial Crisis.