This paper introduces the concept of the "absent curriculum" on the premise that the study of curriculum has been prone to privileging curricular presence to the exclusion of curricular absence. In order to address this imbalance and to articulate a theory of absence in the curriculum, the paper applies ideas derived from the philosophy of critical realism--"absence" and "totality"--to curriculum theory to conceive of the "absent curriculum." The paper outlines three components of the "absent curriculum": the "null curriculum" at the level of national curricular policy, the "unselected curriculum" at the level of school curricular planning and the "unenacted curriculum" at the classroom level of teacher delivery. This conceptual framework is illustrated by a case example of how the absence of the history of Muslim contribution from the teaching of the National Curriculum for history in four English schools formed an "absent curriculum" which prompted some of the research sample of 295 British Muslim boys to disengage from their learning of history. The paper concludes that the "absent curriculum" is a hidden curriculum that suggests to groups whose histories are missing from the national curricula that they are relatively insignificant citizens in the community of the nation.