Chameleon Cosmology proposes that the accelerated expansion of the universe and time-varying fine-structure constant are explained by a scalar field with mass of order H₀, which interacts with matter with couplings of order unity. This field's mass depends on local matter density, making it massive on Earth (1 mm scale) and light in the solar system (10-10⁴ AU). The model satisfies current General Relativity tests but predicts EP violations and fifth-force effects in space, differing from Earth measurements. Scalar fields in this model have drastically different behaviors in high and low density regions, allowing them to evade EP constraints on Earth while influencing cosmological scales. The chameleon field's mass is determined by the interplay of self-interactions and conformal coupling to matter, resulting in an effective potential with a minimum. The model predicts that future gravity experiments will detect significant EP violations and fifth-force effects, providing evidence for this scenario. The field's behavior is governed by an effective potential that depends on local matter density, with the chameleon field's mass and value at the minimum depending on the density. The model satisfies solar system tests of gravity due to the thin-shell suppression of chameleon-mediated forces between large objects. The energy scale M is constrained to be of the order of 1 mm⁻¹, ensuring compatibility with laboratory experiments and cosmological observations.Chameleon Cosmology proposes that the accelerated expansion of the universe and time-varying fine-structure constant are explained by a scalar field with mass of order H₀, which interacts with matter with couplings of order unity. This field's mass depends on local matter density, making it massive on Earth (1 mm scale) and light in the solar system (10-10⁴ AU). The model satisfies current General Relativity tests but predicts EP violations and fifth-force effects in space, differing from Earth measurements. Scalar fields in this model have drastically different behaviors in high and low density regions, allowing them to evade EP constraints on Earth while influencing cosmological scales. The chameleon field's mass is determined by the interplay of self-interactions and conformal coupling to matter, resulting in an effective potential with a minimum. The model predicts that future gravity experiments will detect significant EP violations and fifth-force effects, providing evidence for this scenario. The field's behavior is governed by an effective potential that depends on local matter density, with the chameleon field's mass and value at the minimum depending on the density. The model satisfies solar system tests of gravity due to the thin-shell suppression of chameleon-mediated forces between large objects. The energy scale M is constrained to be of the order of 1 mm⁻¹, ensuring compatibility with laboratory experiments and cosmological observations.