Opus Dei was founded in 1928 by a Spanish priest, Josemaría Escrivá. Escrivá died on June 26, 1975. He was canonized by Pope St. John Paul II on October 6, 2002. You can find out more about St. Josemaría at this site dedicated to spreading information about him.
Opus Dei is a personal prelature of the Roman Catholic Church, composed of both laity and priests, whose purpose is to fulfill a specific pastoral mission under the jurisdiction of its own prelate, who may or may not be a bishop. Personal prelatures are sort of like dioceses, but they consist of people rather than a geographical area. Opus Dei may operate in dioceses around the world, but only with the express permission of the diocesan bishop. Opus Dei reports directly to the Vatican Congregation for Bishops.
Personal prelatures are discussed in Canon Law, canons 294-297.
Personal prelatures were foreseen by Vatican II, largely through the efforts of St. Josemaría, who wanted a juridical structure in the Church which he believed suited Opus Dei better than the old structure of a secular institute. Currently Opus Dei is the only personal prelature in the Church. It was given this status by Pope St. John Paul II in 1983. Hopefully the Holy Spirit will make use of this relatively new and flexible organizational structure in the church and inspire the church to create other personal prelatures to address the various needs of the apostolate.
The specific pastoral mission of Opus Dei is to spread knowledge of the universal call to holiness and to offer its members and others who wish to take part in its activities the assistance they need to become saints in the middle of the world. Members of Opus Dei strive for this sanctity according to Opus Dei’s spirit and practice.
One of the specific characteristics of Opus Dei is its emphasis on one’s work, whatever it is, as a means of sanctification. We are encouraged to see all the circumstances and events of our lives as opportunities to grow in love for the Lord and to serve the Church.
Opus Dei teaches that holiness is not only for priests and nuns. It is the obligation of all Christians to seek holiness. And for lay Christians, we have to seek it right where we are, in the ordinary circumstances of our lives. We don’t seek holiness despite the activities of our ordinary life as lay people, but precisely through those activities. The “stuff” that goes into being a lay person is the very “stuff” that can make us holy. As part of this path to sanctity, members of Opus Dei follow an intense “plan of life” (see Question 6) which focuses on traditional methods of prayer, such as the Rosary, mental prayer, daily Mass, etc.