Before addressing the specific question about the manner of receiving Holy Communion, let’s briefly provide a little context.
 
The Mass has two principal parts, or movements: the Liturgy of the Word followed by the Liturgy of the Eucharist. As the name suggests, the Liturgy of the Word involves the proclamation of Sacred Scripture, further illuminated by the ordained minister in the homily. God’s Word should create in us a burning desire to receive Jesus—the “Word made Flesh”—in Communion (see Luke 24:28-35).
 
The Liturgy of the Eucharist has three parts. First, the gifts are presented and prepared. Then there is the Eucharistic Prayer, during which the gifts are consecrated and become the Body and Blood of Christ. The Liturgy of the Eucharist culminates with the Communion Rite, during which we have the opportunity to receive Jesus in the most intimate way we can in this life.
 
So how does the Church expect us to come forward to receive Jesus during the Communion Rite?
 
The overarching consideration is that we are receiving Christ Himself in Holy Communion. In what the Catechism of the Catholic Church calls “so great and so holy a moment” (no. 1385), Jesus comes to each of us personally as the Bread of Life and the Bridegroom of our souls. So clearly the manner in which we receive Him is not an insignificant matter. And clearly, our external actions should reflect an interior sense of reverence and awe.
 
We must be properly disposed to receive Communion. If we’re aware of having committed a serious sin, we should repent and go to Confession before presenting ourselves for Communion (CCC 1385; cf. 1 Cor. 11:27-29). In addition, the Catechism notes that in preparing for Communion, the faithful should observe the required one-hour fast, and their behavior and even their manner of dress "should convey the respect, solemnity, and joy of the moment when Christ becomes our guest" (CCC 1387).

There are two questions that frequently arise in the context of receiving Holy Communion. First, do we stand, or do we kneel?

The General Instruction of the Roman Missal (“GIRM”) provides that the faithful may receive Communion standing or kneeling, as established by the conference of bishops in a given geographical area. It further says that if the faithful receive standing, they should first make an appropriate gesture of reverence. Kneeling itself is a reverent gesture, so no other sign of reverence is needed when one receives kneeling.
 
Are you with me so far?

The U.S. bishops have specified that the norm for reception of Communion in the United States is standing (GIRM, with U.S. adaptations, no. 160). The Holy See has emphatically added, however, that those who kneel for Communion are not to be chastised, let alone denied the Sacrament, as kneeling for Communion is a praiseworthy traditional practice that beautifully expresses adoration and reverence. Still, the faithful are gently called by legitimate Church authority to stand for Communion.

And since the norm is to receive standing, a “gesture of reverence” should be made before receiving Communion. In recent years the U.S. bishops have established a bow of the head as the gesture the faithful should make immediately before receiving Communion.
 
In my experience, well over 90% of the faithful receive without making any gesture of reverence. Of those that do, many genuflect, make a sign of the cross, or bow deeply from the waist. Certainly those are “gestures of reverence” and are much better than no gesture of reverence, but the Church asks us simply to bow our heads just before receiving Communion.

Next, do we receive on the hand or on the tongue? The brief answer is that the faithful may freely choose either option (leaving aside for now the relatively rare practice of Communion by intinction).

While in many places today Communion in the hand is commonplace, it should be noted that Communion in the hand is an exception to the general norm of Communion on the tongue. Canada, Mexico, the Philippines, and the United States are examples of countries that have been granted permission to deviate from the universal practice of receiving Communion exclusively on the tongue.

The Vatican has further stressed that if one chooses to receive Communion in the hand in a place where it is permitted, due respect for the Sacrament must be retained, which includes (a) coming forward with clean hands; (b) consuming the host before returning to one’s pew; (c) taking care not to lose fragments of the host; and (d) actually receiving the host on the hand rather than taking it directly from the paten or container (i.e., “self-communicating").
 
Next up: Communion from the cup!