The abode of souls excluded from the full blessedness of the beatific vision, but not suffering any other punishment. They enjoy the happiness that would have been human destiny if humans had not been elevated to the supernatural order.
Catholic theology distinguishes two kinds of limbo. The limbo of the Fathers (limbus patrum) was the place where the saints of the Old Testament remained until Christ's coming and redemption of the world. The limbo of infants (limbus infantium) is the permanent state of those who die in original sin but are innocent of any personal guilt.
Regarding the limbo of infants, it is an article of the Catholic faith that those who die without baptism, and for whom the act of baptism has not been supplied in some other way, cannot enter heaven. This is the teaching of the ecumenical councils of Florence and Trent. After defining justification as "a passing from the state in which man is born of the first Adam, to the state of grace and adoption as sons of God," Trent declared, "Since the Gospel was promulgated, this passing cannot take place without the water of regeneration or the desire for it, as it is written, 'Unless a man be born again of water and the Holy Spirit, he cannot enter the kingdom of God' (John 3:5)" (Denzinger 1524).
Some theologians of renown have thought that God might supply the want of baptism by some other means. St. Bernard suggested that such infants could reach heaven because of the faith of their parents (De Baptismo I, 4; II, 1). Cardinal Cajetan (1469-1534) espoused the same theory, but Pope St. Pius V had the passage removed from Cajetan's works.
The great majority of theologians, approved by the Church, teach that infants who die in original sin suffer no "pain of sense." They are simply excluded from the beatific vision. Do they grieve because of heaven? St. Thomas Aquinas answers that they do not, because pain of punishment is proportioned to personal guilt, which does not exist here. Rather, "They rejoice because they share in God's goodness and in many natural perfections" (De Malo, V, 3). It is believed that infants in limbo know and love God intensely by the use of their natural powers, and the enjoy full natural happiness.
The Church has never defined the existence of limbo, although she has more than once supported the fact by her authority. Those who either deny that heaven is a supernatural destiny to which no creature has a natural claim, or who deny that original sin deprives a person of a right to heaven logically also deny the very possibility of limbo. On their premises there is no need of such a place. Among others who denied the existence of limbo were the Jansenists, whose theory of selective predestination excluded the need for any mediatorial source of grace, including baptism. They were condemned by Pope Pius VI as teaching something "false, rash and injurious to Catholic education," because they claimed that it was a Pelagian fable to hold that there is a place "which the faithful generally designate by the name of limbo of children," for the souls of those who depart this life with the sole guilt of original sin (Denzinger 2626). Pope Pius XII declared that "an act of love can suffice for an adult to acquire sanctifying grace and supply for the lack of baptism; to the unborn or newly born infant this way is not open" (Acta Apostolicae Sedis, XLIII, 84). At stake in the traditional belief in limbo is the revealed doctrine that heaven is a sheer gift of divine goodness and that baptism of water or desire is necessary to enter heaven. (Etym. Latin limbo, ablative form of limbus, border; taken from "in limbo patrum" [in the border of hell reserved for the fathers (or saints)], a phrase used by the Church Fathers.)