Occupational exposure limits (OELs) were first introduced more than a century ago in Germany [1]. They were based on observations of people exposed at the workplace, and on experimental exposures of humans and animals, all accompanied by analytical determination of airborne occupational toxicants. The "acceptable concentrations for short-term and long-term exposure" were derived using crude subjective criteria (humans), or gross pathological alterations (animals). Over the years considerable refinement of these criteria has been achieved, both in their type and number, starting from overt histological derangements, going on to the physiological and biochemical level, and even to subtle psychological parameters. This development has taken place in parallel with, and has been considerably influenced by changes in the definition of health and the perception of effects detrimental to health. Differences in the elementary philosophy of health and in the activities aimed at preventing damage to health in different societies have complicated all the efforts to harmonize standard-setting processes at the international level.