This paper reviews various modified gravity theories that serve as gravitational alternatives to dark energy, focusing on $ f(R) $, $ f(G) $, and $ f(R,G) $ gravity, as well as models with non-linear gravitational coupling and string-inspired Gauss-Bonnet-dilaton coupling. These theories are shown to naturally describe the late-time universe's accelerated expansion, including the effective cosmological constant, quintessence, or phantom phases. Some models pass Solar System tests and can explain the coincidence problem through the universe's expansion. The paper discusses the transition from deceleration to acceleration, the possibility of a transient phantom phase, and the role of modified gravity in addressing the hierarchy problem in high-energy physics. It also explores the equivalence of $ f(R) $ gravity with scalar-tensor theory and the dynamics of dark energy in modified gravity. The paper concludes that modified gravity offers a promising framework for understanding dark energy and dark matter, with potential applications in cosmology and high-energy physics.This paper reviews various modified gravity theories that serve as gravitational alternatives to dark energy, focusing on $ f(R) $, $ f(G) $, and $ f(R,G) $ gravity, as well as models with non-linear gravitational coupling and string-inspired Gauss-Bonnet-dilaton coupling. These theories are shown to naturally describe the late-time universe's accelerated expansion, including the effective cosmological constant, quintessence, or phantom phases. Some models pass Solar System tests and can explain the coincidence problem through the universe's expansion. The paper discusses the transition from deceleration to acceleration, the possibility of a transient phantom phase, and the role of modified gravity in addressing the hierarchy problem in high-energy physics. It also explores the equivalence of $ f(R) $ gravity with scalar-tensor theory and the dynamics of dark energy in modified gravity. The paper concludes that modified gravity offers a promising framework for understanding dark energy and dark matter, with potential applications in cosmology and high-energy physics.