Genuflection (or genuflexion), bending at least one knee to the ground, was from early times a gesture of deep respect for a superior. In 328 BC, Alexander the Great introduced into his court etiquette some form of genuflection already in use in Persia. In the Byzantine Empire even senators were required to genuflect to the emperor. In medieval Europe, one demonstrated respect for a king or noble by going down on one knee.
The Latin word genuflectio, from which the English word is derived, originally meant kneeling rather than the rapid dropping to one knee and immediately rising that became customary in Western Europe in the Middle Ages.
From the custom of genuflecting to kings and other nobles arose the custom by which lay people or clergy of lesser rank genuflect to a prelate and kiss his episcopal ring, as a sign of acceptance of the bishop's apostolic authority as representing Christ in the local church.
In the same period, the clergy genuflected when passing before the bishop of the diocese when he presides at a liturgical ceremony. But the officiating priest, as also all prelates, canons, etc., were dispensed, and substituted a bow of the head and shoulders for the genuflection.
The present Catholic liturgical books exclude genuflecting to a bishop during the liturgy: "A genuflection, made by bending the right knee to the ground, signifies adoration, and therefore it is reserved for the Most Blessed Sacrament, as well as for the Holy Cross from the solemn adoration during the liturgical celebration on Good Friday until the beginning of the Easter Vigil." But outside of the liturgy some continue to genuflect or kneel to kiss a bishop's ring.
The practice of genuflecting to the Blessed Sacrament, in particular when arriving or leaving its presence, has grown up only in the Latin Rite Catholic Church, and even there is a relatively modern replacement for the profound bowing down of head and body that is still maintained in the East as the supreme act of liturgical reverence.
It was only during the later Middle Ages, centuries after it had become customary to genuflect to persons in authority, such as bishops, that the practice of genuflecting to the Blessed Sacrament was introduced and gradually spread, becoming viewed as obligatory only from the end of the fifteenth century. 1502 has been given as the date of its formal recognition. For a long time after it became usual to raise the consecrated Host and Chalice after the Consecration so as to show them to the people, no obligatory genuflections accompanied it.
The rule whereby before the Blessed Sacrament unveiled as at Expositions (but not when lying on the corporal during Mass) one genuflected on both knees was altered in 1973, with the introduction of the rule: "Genuflection in the presence of the Blessed Sacrament, whether reserved in the tabernacle or exposed for public adoration, is on one knee."
The Tridentine Mass requires more numerous genuflections to the Blessed Sacrament during Mass.
Genuflection or kneeling is prescribed at various points of the Roman Rite liturgy, such as after the mention of Jesus' death on the cross in the readings of the Passion during Holy Week
A genuflection is made at the mention of the Incarnation in the words et incarnatus est de Spiritu Sancto, ex Maria Virgine, et homo factus est ("by the power of the Holy Spirit he became incarnate of the Virgin Mary, and was made man") in the Creed on the solemnities of Christmas and the Annunciation.
In the Tridentine Mass this genuflection is made on any day on which the Creed is recited at Mass, as well as at several other points:
In the Maronite Catholic Church, there is an evocative ceremony of genuflection on the feast of Pentecost. The congregation genuflects first on the left knee to God the Father, then on the right knee to God the Son, and finally on both knees to God the Holy Spirit.
Some Anglicans and Lutherans also genuflect during their worship services.