This standard specifies minimum performance criteria and testing procedures for instruments and/or systems designed to quantify the concentration of 222Rn gas in air. These are consistent but general performance criteria applicable to the wide variety of radon measurement devices used for indoor measurements, primarily in residential environments or buildings not associated with the possession or handling of radioactive materials. Also included is a description of documentation necessary for demonstration of compliance with this standard. This initial edition of the standard addresses performance criteria for radiological and environmental parameters only.