The history of chemical regulation involved constructing lists of chemicals that were considered too hazardous or too risky and imposing some types of controls on them. Chemical-by-chemical regulation is slow, costly, inefficient, and inadequate. The nature of the concern for a chemical is not based on its chemical name but rather on its combination of properties. Some combinations of properties may lead a chemical to be bioavailable, others to be persistent, still others to be reactive or explosive. Since it is the combination of these properties that cause the concern, it is the properties that should be the basis of regulation. In this way, the chemicals of concern can be addressed proactively while providing certainty to the regulated community and critical guidance to the molecular designers of future products.