I didn't know anything about radon until we moved into a house with a radon mitigation system.  Radon is estimated to cause about 21,000 lung cancer deaths per year and is the second lading cause of lung cancer.  The EPA has a great guide to radon and it includesthe following information:

• How Does Radon Get Into Your Home?
• How to Test Your Home
• What Your Test Results Mean
• How to Lower the Radon Levels in Your Home
• The Risk of Living With Radon
• Radon Risk Charts
• Radon Myths