Abstract: The Harm reduction-movement has clearly gathered momentum since the first conference in Liverpool, both on the scientific as at the political level. Since the first conference, where most participants were grass root workers, there is a clear trend in these conferences to address more and more the scientists, at the cost of the former. We have however to remind ourselves that the strength of the movement has been the combination of the scientists and the workers, united as they were by some common ideology. The always stronger scientific basis for “harm reduction”, as aptly demonstrated in the title of the conference book of the 3rd conference in Melbourne “From faith to science”, may however obscure that our actions have roots in ideology. Now that we become an ever more mixed bunch it is necessary to make our ideologies more explicit. This emphasis on ideology is not to belittle the scientific aspects, but to make clear that no value free science exists. Science, history tells us, is one of the most powerful instruments in political conflicts and so we need to be clear about our ideologies. And the more scientific we become the more obscure our ideological motives, the semiconscious roots of our so called scientific data. It is not that I favour any censorship on ideologies within the harm reduction movement, but clearness about them seems necessary for the health of it. We cannot avoid ideology, even when we are scientific. The main ideology, if any, at the first conference seemed that of the legalisers although this was rarely if ever mentioned, let alone that any arguments were produced in favour of it. The other main ideology with regard to the drug issue, the prohibitionist one, was hardly represented, but five years later even convinced prohibitionist organisations as the ICAA start to embrace harm reduction within the framework of prohibitionism. This visible dichotomy however is more on the level of political approaches than of the basic ideologies supporting those two approaches are manifold. These basic ideologies will be described.