Infidelity and its consequences in the Spanish legislation becomes the object of study in order to elucidate, not only the implications thereof in the current law, but also the historical evolution of the same through the transformation, especially, of the social system. Of particular interest in this study are the consequences of infidelity in the damages derived, infidelity as grounds for divorce, disinheritance, the existence of a previous marriage, the influence of infidelity in marriage annulment, in the custody of children, and its impact in the marriage contract.