With the tobacco industry developing and test marketing a wide array of modified cigarettes and novel nicotine-delivery products, the era of tobacco harm reduction is upon us. Like today's new technologies, two previous generations of cigarette innovation-filtered cigarettes in the 1950s and low tar and nicotine cigarettes in the late 1960s and early 1970s were introduced to offer smokers an ostensibly less hazardous means of smoking, and therefore an alternative to quitting. Both innovations maintained cigarette sales and consequently may well have increased the morbidity and mortality toll of smoking. Will a new generation of harm reduction products improve the public's health, or will the experience of the past half-century be repeated? This paper examines the concept of tobacco harm reduction and describes the variety of methods employed in pursuit of it. Through an examination of the experience with filters and low tar and nicotine cigarettes, and an explicit consideration of today's issues and challenges, the paper focuses attention on the essential dimensions of the contemporary harm reduction debate: how science can establish whether novel products or methods will reduce risks to health for individual smokers, or at least exposures likely to influence risks; how a determination can be made as to the likely population impacts of the introduction and marketing of novel products; how health professionals and consumers can learn the potential and limits of harm reduction; and what role for governmental regulation is possible and desirable.