Both Habermas and Foucault are concerned about the domination of scientific knowledges in modern western societies. They critique science so as to open up space for other knowledges. Despite these similarities, the kinds of critique they carry out differ from each other in a fundamental way. This paper examines the differences of their approaches to knowledge and power. I suggest that Habermas's critique of science can be considered in terms of a juridical model which is guided by the question of how to submit science to the rules of right. ' For him, when science operates within the limits of its own domain, it is seen as lawful, as legitimate; when science transgresses the boundary and invades the domains of others, it is seen as unlawful, as illegitimate. In other words, science is unproblematic when it operates according to the rules of right. In portraying an internal relation between reason and science, Habermas's discourse model further represents science in itself as unproblematic. While science may lend itself to the formation of ideologies and fall prey to power, it is not regarded as internally linked to power, but rather to truth and reason. Foucault's analysis, I contend, can be considered in terms of a strategic model which focuses not so much on the question of right, but rather on the mechanisms through which effects are produced.2 Instead of fixing the legitimacy of science or asking what is the proper domain of a certain Foucault examines the role of certain knowledges in the production of effects of power. From this perspective, he sees that on the one hand, produces knowledges and on the other hand, these knowledges produce effects. That is, there is a mutual production between knowledge and power. Nevertheless, one may ask: what the novelty of Foucault's analysis is, for Habermas could not have overlooked this mutual production of knowledge and power. Habermas is certainly aware of the fact that in late capitalist societies, science lends support to state domination and thus produces effects. On the other hand, he would not deny that the state might encourage the development of science to serve its own domination, and hence there is power's production of knowledge. If Habermas could not be blind to the mutual production of knowledge and power, what challenges does Foucault's analysis pose to Habermas? I argue that Foucault and Habermas have very different views about the ways in which knowledge relates to power. In order to see the challenges that Foucault's work poses to Habermas's theory, one has to look more closely into Foucault's analysis of and knowledge. When Foucault says power produces knowledge, his point is not simply that power, as an external force, encourages knowledge by applying and using it for its own purpose. Instead Foucault shows that constitutes the internal condition of the possibility of certain knowledges. Similarly, when Foucault sees knowledge from a strategic model as part of the totality of means by which is exercised, he does not treat those knowledges as external to the effects produced. Instead they form the internal condition of power, without which the production of effects would not be possible. In contrast to Habermas, Foucault demonstrates that there is an internal rather than external relation between knowledge and power. If knowledge is internally linked to power, it is knowledge rather than false ideologies that produces effects. It is true or truth, that implies power. The problem is no longer falsehood or ideology, but truth. Foucault's work, therefore, not only problematizes but also truth. If truth is problematized, that is, if truth is internally linked to power, what are we going to do with truth? In this essay I shall first discuss Habermas's critique of knowledge. Then I shall examine the challenges that Foucault's analysis of power-knowledge poses to Habermas's critique. …