Filtration and Air Cleaning (FAC) emerged during the20th century as a key and essential component of the art andscience of the control and removal of harmful contaminantsfrom controlled environments. Its development and applicationhas paralleled the advancement of ventilation and temperaturecontrol in built environments. In that process, it has been influencedby a number of societal, technological, industrial, andpolitical factors. This presentation will trace the evolution ofthe growth and maturity of the FAC industry as a response toidentified external influences and needs. These influencingfactors will include the development and maturing of thehealthcare industry; the role of electronics and computerizationin industrial process control; the needs of the militaryestablishment; the development of nuclear capability; theproliferation and wide spread growth of air conditioning in thebuilding environment; the challenge of dealing with increasedcontaminant burden in outdoor air; the emergence of large andhigh-rise building construction; the development of man-madeconstruction components; the developing concern for ecologicaland environmental impacts upon and emitting from thebuilt environment; the powerful concern for proper managementof energy usage and cost; the role and development ofmore precise and applicable test standards for evaluating FACperformance; and the pervasive influence of criminal orterrorist driven attacks employing airborne weapons of massdestruction.