The Home Affordable Refinance Program, or HARP, is designed to help homeowners who are current on their house payments and who want to save money by refinancing at lower mortgage interest rates. Normally, refinancing is a straightforward task. But not when the loan is underwater -- that is, when the home's value has fallen below the mortgage balance. That's where HARP comes in.

HARP allows homeowners to refinance their mortgages even when they're underwater. That's the intention, but the reality has been different. HARP is not mandatory, and borrowers often struggle to refinance their underwater loans. Sometimes they succeed, and sometimes they don't.

When HARP was introduced in early 2009, the Obama administration estimated that millions of homeowners would take advantage of it. The numbers have been lower than that. Recently, HARP's expiration date was extended until the end of 2013.

In this series of articles, Bankrate.com explains who is eligible for HARP refinances, what obstacles borrowers can expect to encounter and how to overcome those barriers.

• Revised HARP could help owners refinance
  The HARP refinance program was a bust. Will a revised HARP let you refi and save money?.
• Refinance while loan rates are rock bottom
  When does a mortgage refinance make sense? Refinance at a lower rate if you plan to be in the home long enough to recoup loan costs.
• 7 good reasons for a mortgage refinance
  Why refi? A refinance can make sense for many reasons, from getting a lower rate to consolidating debt.
• 'Cash-in' refinance activity skyrockets
  The cash-out refinance is going out of fashion. Homeowners chasing low mortgage rates have made the "cash-in" refinance the latest rage.
• Five biggest mistakes to avoid when refinancing
  Envy. Sloth. Overall boneheadedness. They lead folks to make refinancing mistakes. But not you. Because you did your research.