In the history of the Church and of the world, we find evidence of various ways of regarding both the theory and the practice of mercy in interpersonal and social relationships. Each model of mercy emphasizes some particular aspect of doing good to another person, and all are complementary and more completely describe this reality we call mercy in human relationships. In our times we can rediscover each of the models of mercy evident in the history of the Church, and also a false notion of mercy that equates it with a feeling of pity, leniency towards evil, or shattering justice; and we find philosophical currents denying any need for mercy whatsoever. We are also witnessing the birth of a new school of mercy, created by St. Sister Faustina and John Paul II and called by theologians – personalistic. Learning from these schools of mercy will allow one to know the truth of Christian mercy, for the practice of mercy depends on the way it is understood.