I just received this:

I am a student interested in the field of real estate. I understand that a real estate agent makes money on the sale of a property based upon a percentage of the final sale price. I was wondering how a real estate agent makes money on a lease of a rental property?

Thanks for the help, Jim

A landlord lists his property with a real estate agent for a number of reasons. The landlord benefits from the agent's experience and connections, but also because the agent has access to the MLS (or Multiple Listing Service) and other venues for promoting the rental property. 

There are many ways that a rental listing can be charged, but most usually the landlord agrees to pay a portion of the first month's rent to the listing agent.  The more the rent, the higher the commission paid.  Landlords are generally happy to pay this because a listing agent saves them time and money (as compared to ads in the paper plus dealing with calls from unqualified renters).

If the renter has his own agent, the listing agent will pay a predetermined portion of the commission to the selling agent (as the renter's agent is called).  Please let me know if this helps.