This bill amends the General Laws to require radon testing in residential real estate transactions. It defines radon and radon testing, and specifies that residential real estate transactions do not include certain types of sales. The bill requires a radon test to be performed no earlier than one year prior to the closing date of the transaction, and the results must be made available to the parties involved. The selling party is responsible for covering the cost of the radon test, and if requested, must allow the buyer to have an additional test performed at their own expense. If the radon test indicates unsafe levels, a radon mitigation system must be installed by a certified individual prior to the closing, and the selling party is responsible for the cost of installation. After the mitigation system is installed, another radon test must be performed to ensure its effectiveness, and the selling party is responsible for the cost of this test as well. The bill would take effect upon passage.