Trusteeism and the trustee system are practices and institutions within certain parishes of the Catholic Church in the United States, under which laypersons participate in the administration of Ecclesiastical Property. When laypersons are among the trustees, the Church seeks agreement with the civil authorities to have the property administered under principles of canon law.

The Church often appoints deputies who are responsible to herself. Technically, such administrators, whether cleric or lay, are called the "fabric" of the Church (Fabrica Ecclesiae).

In very early times ecclesiastical goods were divided into three or four portions, and that part set aside for the upkeep of the Church began to take on the character of a juridical person. The Eleventh Council of Carthage in 407 requested the civil power to appoint five executors for ecclesiastical property, and in the course of time laymen were called on to take their share in this administration, with the understanding, however, that everything was to be done in the name and with the approbation of the Church.

A number of early and medieval synods have dealt with the administration of curators of ecclesiastical property. The employment of laymen in concert with clerics as trustees became common all over Christendom.

In England such officials were called churchwardens. They were generally two in number, one being chosen by the parish priest, the other by the parishioners, and with them were associated others called sidesmen. The churchwardens administered the temporalities of the parish under the supervision of the bishop, to whom they were responsible. An annual report on the administration of church property was made obligatory in all countries by the Council of Trent: "The administrators, whether ecclesiastical or lay, of the fabric of any church whatsoever, even though it be a cathedral, as also of any hospital, confratemity, charitable institution called mont de piété, and of any pious places whatsoever, shall be bound to give in once a year an account of their administration to the Ordinary."

The fabric of the church is distinct from the foundation of the benefice, and sometimes the fabric, in addition to the goods destined for the upkeep of divine worship, possesses also schools and eleemosynary institutions. All lay trustees must be approved by the bishop, and he retains the right of removing them and of overseeing the details of their administration.

In countries in which the church organization was entirely swept away by Protestant Reformation period, as in the British Isles, laymen are less generally employed. In Holland, laymen were admitted to a share in the administration of church temporalities by a decree of the Propaganda. The bishop is to nominate the members of the board, over which the parish priest is to preside. Trustees hold office for four years and may be reappointed at the expiration of that term. When a vacancy occurs the board presents two names to the bishop, from which he selects one. In necessary cases the bishop may dismiss any member and even dissolve the entire board of trustees. In this instance, as in all others where laymen are in question, the Holy See is careful to guard the prescriptions of the sacred canons as to the management and ownership of church goods (see administrator (of ecclesiastical property)).

In the United States the employment of lay trustees was customary in some parts of the country from a very early period. The practice of lay trusteeism in Catholic parishes was influenced by the polity of Congregational churches. Dissensions sometimes arose with the ecclesiastical authorities, and the Holy See has intervened to restore peace. Pope Pius VII vindicated the rights of the Church as against the pretensions of the trustees, and Pope Gregory XVI declared: "We wish all to know that the office of trustees is entirely dependent upon the authority of the bishop, and that consequently the trustees can undertake nothing except with the approval of the ordinary."