What are the rules for fasting before communion?

The rules for fasting before Communion are fairly simple, but there is a surprising confusion about it. While the rules for fasting before Communion have changed over the centuries, the last change occurred over 50 years ago. Before then, a Catholic who wished to receive Holy Communion had to fast from midnight onwards. What are the current rules for fasting before Communion?

The current rules for fasting before communion
The current rules were introduced by Pope Paul VI on November 21, 1964 and are found in Canon 919 of the Code of Canon Law:

A person who is to receive the Most Holy Eucharist must abstain from food and drink for at least an hour before holy communion, except only water and medicines.
A priest who celebrates the Most Holy Eucharist two or three times on the same day can take something before the second or third celebration even if there is less than an hour between them.
The elderly, the sick and those who take care of them can receive the Holy Eucharist even if they ate something in the previous hour.
Exceptions for the sick, the elderly and those who take care of them
As for point 3, "senior" is defined as 60 years or older. In addition, the Congregation of the Sacraments published a document, Immensae caritatis, on January 29, 1973, which clarifies the terms of the fast before Communion for "the sick and those who take care of them":

To recognize the dignity of the sacrament and to arouse joy at the coming of the Lord, it is good to observe a period of silence and recollection. It is a sufficient sign of devotion and respect from the sick if they direct their mind for a short time to this great mystery. The duration of the Eucharistic fast, that is, of abstention from food or alcoholic drink, is reduced to about a quarter of an hour for:
the sick in health facilities or at home, even if they are not bedridden;
the faithful of advanced years, whether they are confined to their homes because of old age or who live in homes for the elderly;
sick priests, even if not bedridden, and elderly priests, both to celebrate Mass and to receive communion;
the people who take care, as well as family and friends, of the sick and the elderly who wish to receive communion with them, whenever these people are unable to maintain a fast hour without inconveniences.

Communion for the dying and those in danger of death
Catholics are exempted from all the rules of fasting before Communion when they are in danger of death. This includes Catholics who are receiving Communion as part of the Last Rites, with Confession and Anointing of the Sick, and those whose lives may be in imminent danger, such as soldiers who receive Communion at Mass before going into battle.

When does a fast hour start?
Another frequent point of confusion concerns the start of the clock for the Eucharistic fast. The hour mentioned in canon 919 is not an hour before mass, but, as they say, "an hour before holy communion".

This does not mean, however, that we should bring a stopwatch to church, or try to understand the first point at which Communion could be distributed at Mass and end our breakfast exactly 60 minutes earlier. Such behavior lacks the fasting point before Communion. We must use this time to prepare ourselves to receive the Body and Blood of Christ and to remember the great sacrifice that this sacrament represents.

Extension of the Eucharistic fast as a private devotion
Indeed, it is a good thing to choose to extend the Eucharistic fast if you are able to do so. As Christ himself said in John 6:55, "For my flesh is true food and my blood is true drink." Until 1964, Catholics fasted from midnight onwards when they received Communion, and from apostolic times Christians have tried, whenever possible, to make the Body of Christ their first food of the day. For most people, such a fast would not be an overwhelming burden and could bring us closer to Christ in this most holy sacrament.