The Equivalence Principle

Abstract We review the conceptual basis on the Equivalence Principle, elucidating its crucial role in the formulation of gravitational theories. We analyze the direct consequences of the principle by reinterpreting in a relativistically coherent manner the way it should be considered in the derivation of gravitational redshift by using the relativistic Doppler effect. Einstein missed out this point. The most important experiments already carried out in the search for violations of the equivalence between gravitational mass and inertial mass are reviewed, their operational principles and results are analyzed.