In this essay, the author analyzes two theoretical perspectives--incorporation and abjection--that inform official knowledge generally and high school American history textbooks specifically. While contemporary textbooks increasingly depict the experiences of historically marginalized groups such as women, African Americans, Latinos, American Indians, and the poor, they continue to incorporate these groups through the restrictive practice of mentioning, which limits possible resistant teachings and/or readings of American history. In addition to discussing the limiting function of incorporation, the author also argues that textbooks abject knowledge deemed unfit for the curricular body of official knowledge and the selective tradition of American history. The psychoanalytic theory of abjection is the other side of incorporation and the contribution this essay makes to existent scholarship on official knowledge and textbooks. (Contains 33 footnotes.)