This review summarizes recent progress in massive gravity, focusing on theories that extend general relativity (GR) by introducing a massive spin-2 field (the graviton). The review begins by showing how different massive gravity theories emerge from higher-dimensional general relativity, leading to the Dvali–Gabadadze–Porrati (DGP) model, cascading gravity, and ghost-free massive gravity. It then explores the theoretical and phenomenological consistency of these models, proving the absence of Boulware–Deser ghosts and reviewing the Vainshtein mechanism and cosmological solutions. The review also presents alternative models such as new massive gravity, Lorentz-violating massive gravity, and non-local massive gravity. The review discusses the challenges of massive gravity, including the five degrees of freedom of a massive spin-2 field and the vDVZ discontinuity. It explains how the Vainshtein mechanism screens the extra degree of freedom in the massless limit, allowing for a consistent theory. The review also addresses the Boulware–Deser ghost, which is avoided in models such as DGP and ghost-free massive gravity (dRGT). It discusses the decoupling limit of massive gravity, where the theory becomes non-linear and non-renormalizable, and explores extensions such as mass-varying gravity, quasi-dilaton gravity, and partially massless gravity. The review also covers the Vainshtein mechanism, which allows for a non-linear theory of massive gravity without the Boulware–Deser ghost. It discusses the phenomenological aspects of massive gravity, including gravitational waves, solar system tests, lensing, pulsars, black holes, and cosmology. The review concludes with other related theories of massive gravity, including new massive gravity, Lorentz-violating massive gravity, and non-local massive gravity. The review emphasizes the importance of massive gravity as an alternative to GR and its potential for new observational signatures.This review summarizes recent progress in massive gravity, focusing on theories that extend general relativity (GR) by introducing a massive spin-2 field (the graviton). The review begins by showing how different massive gravity theories emerge from higher-dimensional general relativity, leading to the Dvali–Gabadadze–Porrati (DGP) model, cascading gravity, and ghost-free massive gravity. It then explores the theoretical and phenomenological consistency of these models, proving the absence of Boulware–Deser ghosts and reviewing the Vainshtein mechanism and cosmological solutions. The review also presents alternative models such as new massive gravity, Lorentz-violating massive gravity, and non-local massive gravity. The review discusses the challenges of massive gravity, including the five degrees of freedom of a massive spin-2 field and the vDVZ discontinuity. It explains how the Vainshtein mechanism screens the extra degree of freedom in the massless limit, allowing for a consistent theory. The review also addresses the Boulware–Deser ghost, which is avoided in models such as DGP and ghost-free massive gravity (dRGT). It discusses the decoupling limit of massive gravity, where the theory becomes non-linear and non-renormalizable, and explores extensions such as mass-varying gravity, quasi-dilaton gravity, and partially massless gravity. The review also covers the Vainshtein mechanism, which allows for a non-linear theory of massive gravity without the Boulware–Deser ghost. It discusses the phenomenological aspects of massive gravity, including gravitational waves, solar system tests, lensing, pulsars, black holes, and cosmology. The review concludes with other related theories of massive gravity, including new massive gravity, Lorentz-violating massive gravity, and non-local massive gravity. The review emphasizes the importance of massive gravity as an alternative to GR and its potential for new observational signatures.