This document provides a summary of radon and recommendations for testing homes for radon. It notes that radon is a radioactive gas that can cause lung cancer, with an estimated 21,000 lung cancer deaths per year in the US. It recommends that all homes be tested for radon using inexpensive test kits, and that high radon levels above 4 pCi/L be fixed. It provides information on how radon enters homes and how to conduct both short-term and long-term radon tests.