Clifford M. Will reviews the experimental tests of general relativity (GR) and the theoretical frameworks used to analyze them. The Einstein equivalence principle (EEP), which includes the weak equivalence principle (WEP), local Lorentz invariance (LLI), and local position invariance (LPI), is well supported by experiments such as the Eötvös experiment, tests of special relativity, and gravitational redshift experiments. Ongoing tests aim to detect new interactions from unification or quantum gravity. GR has been tested at the post-Newtonian level with high precision, including light deflection, Shapiro time delay, Mercury's perihelion advance, and the Nordtvedt effect in lunar motion. Gravitational-wave damping has been detected in the Hulse-Taylor binary pulsar, agreeing with GR to better than half a percent. Future tests will come from direct observation of gravitational radiation from astrophysical sources. The history of experimental relativity is divided into four periods: Genesis, Hibernation, a Golden Era, and the Quest for Strong Gravity. The Golden Era (1960–1980) saw systematic efforts to test GR predictions and compare them with alternative theories. Since 1980, the field has focused on strong gravity, with experiments probing extreme gravitational fields. The Eötvös ratio measures WEP violations, with high-precision experiments like the Eöt-Wash reaching 3×10⁻¹³. Projects like MICROSCOPE and STEP aim to test WEP to 10⁻¹⁵ and 10⁻¹⁸, respectively. Tests of LLI involve measuring the isotropy of the speed of light and the isotropy of atomic energy levels. The Hughes-Drever experiments and later laser-cooled atom experiments have placed bounds on Lorentz violations. The Standard Model Extension (SME) provides a framework for testing Lorentz invariance with many parameters. Astrophysical observations also help bound Lorentz violations, such as through photon dispersion relations. Tests of LPI involve gravitational redshift experiments, measuring frequency shifts between clocks at different heights. The Pound-Rebka-Snider experiments measured the redshift of gamma-ray photons with high precision. More recent experiments, like the Vessot-Levine rocket experiment, have placed bounds on the LPI violation parameter α. The most precise bound so far is |α| < 2.1×10⁻⁵. Experiments also test variations in fundamental constants over time, such as the electromagnetic fine structure constant α_EM. Observations of quasar absorption lines and the Oklo phenomenon have placed bounds on α_EM variations. The Oklo reactors provided a natural laboratory to test the constancy of fundamental constants over billions of years. Theoretical frameworks, such as the THεμ formalism, provide a way to analyze EEP violations. Schiff's conjecture suggestsClifford M. Will reviews the experimental tests of general relativity (GR) and the theoretical frameworks used to analyze them. The Einstein equivalence principle (EEP), which includes the weak equivalence principle (WEP), local Lorentz invariance (LLI), and local position invariance (LPI), is well supported by experiments such as the Eötvös experiment, tests of special relativity, and gravitational redshift experiments. Ongoing tests aim to detect new interactions from unification or quantum gravity. GR has been tested at the post-Newtonian level with high precision, including light deflection, Shapiro time delay, Mercury's perihelion advance, and the Nordtvedt effect in lunar motion. Gravitational-wave damping has been detected in the Hulse-Taylor binary pulsar, agreeing with GR to better than half a percent. Future tests will come from direct observation of gravitational radiation from astrophysical sources. The history of experimental relativity is divided into four periods: Genesis, Hibernation, a Golden Era, and the Quest for Strong Gravity. The Golden Era (1960–1980) saw systematic efforts to test GR predictions and compare them with alternative theories. Since 1980, the field has focused on strong gravity, with experiments probing extreme gravitational fields. The Eötvös ratio measures WEP violations, with high-precision experiments like the Eöt-Wash reaching 3×10⁻¹³. Projects like MICROSCOPE and STEP aim to test WEP to 10⁻¹⁵ and 10⁻¹⁸, respectively. Tests of LLI involve measuring the isotropy of the speed of light and the isotropy of atomic energy levels. The Hughes-Drever experiments and later laser-cooled atom experiments have placed bounds on Lorentz violations. The Standard Model Extension (SME) provides a framework for testing Lorentz invariance with many parameters. Astrophysical observations also help bound Lorentz violations, such as through photon dispersion relations. Tests of LPI involve gravitational redshift experiments, measuring frequency shifts between clocks at different heights. The Pound-Rebka-Snider experiments measured the redshift of gamma-ray photons with high precision. More recent experiments, like the Vessot-Levine rocket experiment, have placed bounds on the LPI violation parameter α. The most precise bound so far is |α| < 2.1×10⁻⁵. Experiments also test variations in fundamental constants over time, such as the electromagnetic fine structure constant α_EM. Observations of quasar absorption lines and the Oklo phenomenon have placed bounds on α_EM variations. The Oklo reactors provided a natural laboratory to test the constancy of fundamental constants over billions of years. Theoretical frameworks, such as the THεμ formalism, provide a way to analyze EEP violations. Schiff's conjecture suggests