Personal prelature is an institutional structure of the Roman Catholic Church which comprises a prelate, clergy and possibly laity who undertake specific pastoral activities. Personal prelatures, similar to dioceses and military ordinariates, are under the governance of the Vatican's Congregation for Bishops. These three types of ecclesiastical structures are composed of lay people served by their own secular clergy and prelate. Unlike dioceses which cover territories, personal prelatures —like military ordinariates— take charge of persons as regards some objectives regardless of where they live.
In the Roman Catholic Church, the personal prelature was conceived during the sessions of the Second Vatican Council in no. 10 of the decree Presbyterorum ordinis and was later enacted into law by Paul VI in his motu proprio Ecclesiae sanctae. The institution was later reaffirmed in the 1983 Code of Canon Law.
A personal prelature is an institution having clergy and (possibly) lay members which would carry out specific pastoral activities. The adjective personal refers to the fact that, in contrast with previous canonical use for ecclesiastical institutions, the jurisdiction of the prelate is not linked to a territory but over persons wherever they happen to be. The establishment of personal prelatures is an exercise of the theologically inherent power of self-organization which the Church has to pursue its mission, though a personal prelature is not a particular church as dioceses and military ordinariates are.
Many features of a personal prelature may seem similar to religious orders. For starters, the prelate governs the prelature with ordinary power and is selected according to the statutes of the prelature (can. 295), which could mean election by the members of the prelature or some other method. Also, the clergy of the prelature also are incardinated into the prelature itself as opposed to the local particular church (ibid).
However, the laity and clergy of the prelature do not take the three vows which members of religious orders take. It is also possible for the clergy of the prelature to have a different relationship with the local ordinary than members of religious orders (can. 297) since, normally, religious orders are not exempt from the laws and the governance of the particular church where they live and work. Thirdly, the prelature defines its relationship with the laity dedicated to its mission, which could mean canonical membership or a relationship defined by mutual agreement (can. 296). For religious orders, however, laity may be incorporated as tertiaries, that is, members of the order, who live according to its spirit and life in their secular and family settings, while not being required to take the vows of the order. It is notable that tertiaries, who collectively comprise the third order of the major orders of the Church, have histories going back many centuries, and are thus a much more established venue through which laity are active. Finally, the prelate may be a bishop, which generally does not happen in a religious order. For these and other reasons, personal prelatures are clearly different from religious institutes and the consecrated life in general, as well as from associations and movements of the faithful.
In a nutshell: personal prelatures are fundamentally secular organizations operating in the world (members take no vows and live normal, everyday lives), whereas religious orders are religious organizations operating out of the world (members take vows and lead lives in accordance with their specific organization).
The first, and thus far the only, personal prelature is Opus Dei, which was established as a personal prelature by Pope John Paul II in 1982 through the Apostolic constitution Ut sit. In the case of Opus Dei, the prelate is elected by members of the prelature and confirmed by the Pope, the laity and clergy of the prelature are still under the governance of the particular church where they live, and the laity associated with the prelature (both men and women) are organically united under the jurisdiction of the prelate.
It was speculated that in case of a reconciliation of the Society of St. Pius X, the same status of personal prelature could be conferred upon that priestly institute to facilitate its pastoral activities in dioceses from which they are independent.
Related structure of personal ordinariate
On October 20, 2009, it was announced that the Holy See would create personal ordinariates for Anglicans entering the Catholic Church. These new structures would presumably be inspired by existing military ordinariates, in ways that are comparable to the current Opus Dei personal prelature. 
- ↑ Personal Prelatures cann. 294–297,
- ↑ Note of the CDF about personal ordinariates for Anglicans entering the Catholic Church