Michel Foucault (1926-84) is a primary thinker informing the construction of a critical theory of library and information science (LIS), or librarianship. He is widely cited and is adapted in various ways that focus on LIS forms of power, discourse, and so on. Others have addressed Foucault's topics, but he remains central. Librarianship has taken up a prior challenge to more fully explore his work, and it is now time to carefully review the implications of Foucault's thinking as a foundation for a critical-theoretical LIS. Foucault has undergone extensive analysis and critique, and this article is a similar step within LIS. While not comprehensive, a review of Foucauldian ideas within LIS literature from a core group of authors is undertaken. Critiques and problems in Foucault's thinking are reviewed since, by relying on Foucault's insights for a line of analysis and research, this LIS theoretical work will reflect some of those same problems.