Viri Probati
Clerical celibacy is the discipline by which, in some Churches, only unmarried men are, as a rule, to be ordained to the priesthood. The same discipline holds in some other Churches for ordination to the episcopate.
Chief of the Catholic particular Churches that follow this discipline is the Latin Rite, but, among the Eastern Catholic Churches, at least the Ethiopic Catholic Church, applies it also.
In this context, "celibacy" retains its original meaning of "unmarried". Though even the married may observe continence, abstaining from sexual intercourse, the obligation to be celibate is seen as a consequence of the obligation to observe perfect and perpetual continence for the sake of the Kingdom of heaven. Advocates see clerical celibacy as "a special gift of God by which sacred ministers can more easily remain close to Christ with an undivided heart, and can dedicate themselves more freely to the service of God and their neighbour."
Throughout the Catholic Church, East as well as West, a priest may not marry. To become a married priest, one must therefore marry before being ordained.
The Catholic, Eastern Orthodox and Oriental Orthodox Churches, without exception, rule out ordination of married men to the episcopate.
The law of clerical celibacy is considered to be not a doctrine, but a discipline. Exceptions are sometimes made, especially in the case of Protestant clergymen who convert to the Catholic Church, and the discipline could in theory be changed for all ordinations to the priesthood.
Read more about Viri Probati: Historical Origins, Theological Foundations, Scriptural Foundations, Eleventh-century Developments, Eastern Catholic Churches, Controversy, Since The Second Vatican Council, Exceptions