Given the numerous conceptual approaches to understanding inclusive education, there is an obvious risk of fragmentation and stagnation in the field. In response, this paper aims to contribute to advancement by going beyond previous work and developing a holistic formulation of inclusive education. Its starting point is that the persistent challenge of offering equal opportunities and full participation for all students in regular schools appears to have complex causal explanations on "multiple levels," including the ideological/political, practical, and individual/subjective. This holistic formulation draws on analyses of (a) the connections between inclusive education, student diversity and the concept of special educational needs, (b) some problematic experiences from Norway, and (c) the current state of the field. In this formulation, three core values of inclusion -- "welcoming communities," "combating discriminatory attitudes," and "education for all" -- as articulated in the Salamanca Declaration, are linked to the institutional practice principles of "participation," "human diversity," and "differentiation." The discussion explores these values and their alignment with the principles of inclusive practice and students' inclusionary outcome in school. Furthermore, the interplay among these values and their corresponding principles of practice principle is illustrated, emphasising the need for awareness when prioritising one over another, both in research and practice.