When did Christ institute the Eucharist?

Christ Instituted the Holy Eucharist on the evening before his death, "on the night when he was betrayed" (1 Corinthians 11:23), when he gathered the Apostles around him in the Upper Room in Jerusalem and celebrated the Last Supper with them.

"For I received from the Lord what I also delivered to you, that the Lord Jesus on the night when he was betrayed took bread, and when he had given thanks, he broke it, and said 'This is my body, which is for you. Do this in remembrance of me.' In the same way also the chalice, after supper, saying, 'This chalice is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me' (1 Corinthians 1123:25).

This, the oldest account of the events in the Upper Room at the last Supper, is by the Apostle Paul, who was not an eyewitness himself, but rather wrote down what was being preserved as a holy mystery by the young Christian community and was being celebrated in the liturgy.

The celebration of the Eucharist is the heart of the Christian communion. In it the Church becomes Church. We are not Church because we get along well, or because we happen to end up in the same parish community, but rather because in the Eucharist we receive the Body of Christ and are increasingly being transformed into the Body of Christ.