Equity, diversity, inclusion, and belonging (EDIB) are central, yet contested, concerns within tourism research. Race and ethnicity are foundational dimensions of this broader agenda, but remain under-theorised. Drawing on a systematic review of 287 peer-reviewed articles published across 85 journals over five decades, this article traces the field's evolution from early marginality- and ethnicity-based explanations to more recent engagements with agency, critical race theory, intersectionality, postcolonialism, and activism. The article argues that, despite this conceptual advancement, the literature remains ontologically fragmented, often examining particular layers of reality (e.g. lived experiences, organisational practices, and structural conditions) in isolation without sufficiently explaining how these layers connect or causally produce the inequalities they document. To address this limitation, it proposes a layered ontological framework informed by critical realism, integrating empirical, actual, and real domains with the dynamics of agency, structure, and relational emergence. Rather than displacing existing theoretical approaches, the framework provides an explanatory architecture through which they may be connected, thereby advancing a more cumulative, multi-level theorisation of how EDIB outcomes are produced, re- and co-produced, and transformed in tourism contexts.