Pax (Lat., peace), an instrument anciently used in the Roman Catholic church, and retained for some time in the church of England. In the early ages of Christianity it was customary for the faithful at certain parts of the divine service to practise literally St. Paul's recommendation, " Greet ye one another with a holy kiss," as appears from the " Apostolical Constitutions " (viii. IX): " Let the bishop salute the church and say, 'The peace of God be with you all;' and let the people answer,' And with thy spirit.' Then let the deacon say to all, ' Salute one another with a holy kiss;' and let the clergy kiss the bishop, and the laymen the laymen, and the women the women." But in course of time, when the separation of the sexes in the church ceased to be observed, a small tablet called the pax, the tabula pads (tablet of peace), or the osculatorium, bearing the image of Christ crucified, or of the Lamb, was kissed first by the bishop, then by the inferior clergy, and finally by the people. The ceremony called giving the pax, as performed in Roman Catholic churches at the present day, is merely a relic of the old custom.

Just before the communion at solemn high masses the officiating clergyman turns to the deacon, and, extending his hands and touching him on the arms, inclines his head toward the deacon's left shoulder, saying, Pax tecum (" Peace be with thee"); to which the deacon answers, Etcum spiritu tuo (" And with thy spirit "). The deacon gives the pax in the same manner to the subdeacon, and each of the inferior ministers to the one next below him in dignity. The people have no part in it. When solemn high mass is celebrated in the presence of the bishop, the celebrant, after giving in this manner the kiss of peace to the deacon, kisses a pax presented to him by the latter, which is then borne to the bishop, who kisses it in turn, and then imparts the peace to his assistants.