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Question about MBS and how it pays
A security is a class of financial instrument you can trade on the market.  A share of stock is a kind of security, for example, as is a bond. In the case of your mortgage, what happens: You take out a loan for $180k.  The loan has two components. a.  The payment stream (meaning the principal and the interest) from the loan b.  The servicing of the loan, meaning the company who is responsible for accepting payments, giving the resulting income to whomever owns it. Many originating banks, such as my initial lender, do neither of these things - they sell the payment stream to a large bank or consortium (often Fannie Mae) and they also sell the servicing of the loan to another company. The payment stream is the primary value here (the servicing is worth essentially a tip off the top).  The originating bank lends $180k of their own money.  Then they have something that is worth some amount - say $450k total value, $15k per year for 30 years - and they sell it for however much they can get for it.  The actual value of $15k/year for 30 years is somewhere in between - less than $450k more than $180k - since there is risk involved, and the present value is far less.  The originating bank has the benefit of selling that they can then originate more mortgages (and make money off the fees) plus they can reduce their risk exposure. Then a security is created by the bigger bank, where they take a bunch of mortgages of different risk levels and group them together to make something with a very predictable risk quotient.  Very similar to insurance, really, except the other way around.  One mortage will either default or not at some % chance, but it's a one off thing - any good statistician will tell you that you don't do statistics on n=1.  One hundred mortgages, each with some risk level, will very consistently return a particular amount, within a certain error, and thus you have something that people are willing to pay money on the market for.