This paper traces the different historical routes which the public health concept of "harm reduction" has taken for illicit drugs and for tobacco and nicotine. It locates these different recent histories, not just in degrees of dangerousness or risk, but rather in the ways in which those concepts have been mediated through intervening factors. It identifies institutional and cultural/conceptual planes for discussion. Key issues include different routes of medicalization; the role of differing policy communities; changing cultural and class positioning; and the shifting of boundaries between categories of "substance," "drug," and "medicine." [Translations are provided in the International Abstracts Section of this issue.]