The Second Vatican Council
Dogmatic Constitution Lumen Gentium, no. 29

At a lower level of the hierarchy are deacons, upon whom hands are imposed "not unto the priesthood, but unto a ministry of service." For strengthened by sacramental grace, in communion with the bishop and his priests, they serve in the diaconate of the liturgy, of the word, and of charity to the people of God.

It is the duty of the deacon, according as it shall have been assigned to him by competent authority, to administer baptism solemnly, to be custodian and dispenser of the Eucharist, to assist at and bless marriages in the name of the Church, to bring Viaticum to the dying, to read Sacred Scripture to the faithful, to instruct and exhort the people, to preside over the worship and prayer of the faithful, to administer sacramentals, and to officiate at funeral and burial services.

Dedicated to duties of charity and of administration, deacons are mindful of the admonition of Blessed Polycarp: "Be merciful, diligent, walking according to the truth of the Lord, who became the servant of all."

Paul’s Letter to Timothy
1 Timothy 3:8-11, 13

Similarly, deacons must be dignified, not deceitful, not addicted to drink, not greedy for sordid gain, holding fast to the mystery of the faith with a clear conscience.  Moreover, they should be tested first; then, if there is nothing against them, let them serve as deacons.  Deacons may be married only once and must manage their children and their households well.  Thus those who serve well as deacons gain good standing and much confidence in their faith in Christ Jesus.

Other documents:

Worldwide Statistics on the Diaconate

Deacon Digest

Resource Guide