A new review provides an introduction and overview of holographic approaches to quantum chromodynamics (QCD) and hadron structure. The gauge/gravity duality allows strongly coupled problems in quark and gluon theory to be recast as geometric descriptions in an extra dimension, where calculations become more tractable.

The paper surveys the predictions of top-down and bottom-up models for the phenomenology of mesons, baryons and glueballs. In the first case, the focus is on the model arising from probing the Witten model of low-energy Yang-Mills theory with flavor branes. In the second, it centers on minimal phenomenological models built on five-dimensional anti-de Sitter space.

The distinction between the two approaches is key: top-down models start from concrete formulations of string theory and inherit their structure, while bottom-up models are designed to reproduce experimental data with the minimal geometric apparatus. Both seek to describe how confined constituents shape the observable properties of hadrons.

The work is conceived as an entry point for researchers and students who want to understand how holography provides tools for the non-perturbative problem of QCD, a field where traditional analytical methods reach clear limits.