As an aside to our survey of the variety of options available for internally organizing a Catholic diocese, let us briefly address the notion of the quasi-parish. The current law makes only one reference to such an institution, in canon 516, and the provisions therein are mostly non-elucidating on their face. This makes a fascinating study for canonists, and is also of potential interest to diocesan bishops in places where, because expanding or shifting populations are presenting difficulties or impossibilities in the delivery of pastoral care through the existing established parishes, such structures which are “not yet parishes” could be useful to consider. But the extant commentary seems clear that the designation is not to be used in reverse: it is not possible to ‘reduce’ an existing parish to quasi-parish status as the law is currently configured.
A quasi-parish is on the way to becoming a parish; it would make no sense to form an already existing parish into an entity which by design is destined to become the parish it had previously been. Rather, if circumstances indicate that a stable community no longer has the characteristics to be a parish, the diocesan bishop would address the dilemma in some other way (e.g., he may unite the parish to a neighboring parish: cf. c. 121).
In the United States at least, many rural dioceses are likely still familiar with the appellation of “mission church” or “mission parish” applied to small worship sites (and their attendant faith communities) served pastorally by the parochus of a larger, more-or-less nearby community. But this is not an official or fixed designation, and has no definition in the law. “Such a church may simply be another worship site within a parish, in which case it would be a non-parochial church. It may, however, belong to what the 1983 Code calls a quasi-parish, which has the characteristics identified in canon 516, §1 and would be a community ‘not yet’ erected as a parish.” In my own diocese, the term “mission” was used until quite recently to describe — for the purposes of internal diocesan pastoral planning — each of several smaller parishes which were served by a priest who was also parochus of another neighboring parish (i.e. a c. 526 §1 situation). In these cases, the so-called mission parish was, ultimately, a canonical territorial parish in its own right, and the terminology conveyed nothing useful beyond a constant reminder that one community was smaller (and probably less vital) than another.
While the quasi-parish seems to be of limited and even unlikely utility in most of the North American context, it is worth noting that the Apostolic Constitution Anglicanorum coetibus may provide a new (if limited) catalyst for the erection of quasi-parishes. Article 14 §3 of the Complementary Norms that accompany AC reads: “For the pastoral care of the faithful who live within the boundaries of a Diocese in which no personal parish has been erected, the Ordinary, having heard the opinion of the local Diocesan Bishop, can make provisions for quasi-parishes (cf. CIC, can. 516, §1).” If and how this provision will be employed as these new Ordinariates unfold, and to what effect, will be one of the many canonically-interesting aspects of these new structures that I will be keeping a close eye on in the coming years.
 For a fairly exhaustive survey of the available commentary on the subject of the quasi-parish see John Renken, “The Quasi-Parish: A Definite Community of the Christian Faithful in a Particular Church,” in Studia canonica, 43 (2009), pp. 27-46.
 Renken, “The Quasi-Parish,” pp. 37-38, note 38.
 Renken, “Parishes and Pastors [cc. 515-544],” in J.P. Beal, J.A. Coriden, T.J. Green (eds.), New Commentary on the Code of Canon Law, commissioned by the Canon Law Society of America, New York and Mahwah, NJ, Paulist Press, 2000, p. 682.
 Congregation for the Doctrine of the Faith, Complementary Norms for the Apostolic Constitution Anglicanorum coetibus, in AAS, , English translation in