Catholic ecclesiology is the theological study of the Catholic Church, its nature, organization and its "distinctive place in the economy of salvation through Christ". Such study shows a progressive development over time being further described in revelation or in philosophy. Here the focus is on the time leading into and since the Second Vatican Council (1962–1965).

Pope Paul VI stressed the importance of the church's self-knowledge in his first encyclical letter, Ecclesiam Suam:

We are convinced that the Church must look with penetrating eyes within itself, ponder the mystery of its own being, and draw enlightenment and inspiration from a deeper scrutiny of the doctrine of its own origin, nature, mission, and destiny.

The doctrine of Communitas Perfecta ("Perfect Community") or Societas Perfecta ("Perfect Society") teaches that the Church is a self-sufficient or independent society which already has all the necessary resources and conditions to achieve its overall goal (final end) of the universal salvation of all peoples. It has historically been used in order to best define Church-State relations. Its origins are in Aristotelian political philosophy, although its adaptation to ecclesiology was done by the Scholastics. The doctrine was widely used in Neoscholastic circles before the Second Vatican Council.

This approach of Pius XII moved beyond the "perfect society" model to the "Mystical Body of Christ", a historical designation explained more fully in this document, identifying the Body of Christ with the Catholic Church in a way that would be repeated by the Second Vatican Council. Lumen gentium, after mentioning "Christ, present to us in His Body, which is the Church" (14), goes on to speak of those who are fully incorporated (14), conjoined (15), and related (16) to the Church. This more expansive idea of the Church is developed in the second chapter of Lumen gentium on the "People of God".

The council's decree on ecumenism, Unitatis redintegratio, declares that “The Spirit of Christ has not refrained from using [separated churches and communities] as a means of salvation” (para. 3). This goes beyond the statement in Mystici corporis Christi that says of non-Catholics that “by an unconscious desire and longing they have a certain relationship with the Mystical Body of the Redeemer” (para. 103). Pius XII can be said to have popularized the notion of the Church as the Body of Christ, which was already present in the writings of Saint Paul in the New Testament.

The second chapter of Lumen gentium is entitled "On the People of God". “People” avoids membership disputes: there are various ways of association; see "Body of Christ" above, which comes from this chapter. Since this chapter of Lumen gentium comes before Chapter 3 "On the Hierarchical Structure of the Church and in particular on the Episcopate", commentators note that it turns the focus from the hierarchy to the laity, declaring that the Holy Spirit "distributes special graces among the faithful of every rank. By these gifts He makes them fit and ready to undertake the various tasks and offices which contribute toward the renewal and building up of the Church" (12).

This is described as a "welcoming judgment on a great mass of theoretical and practical experimentation clamoring for recognition… . The Church´s life does not flow down from Pope thru BB and clergy to a passive laity.^{[clarification needed]} It springs up from the grass-roots of the People of God, and the function of authority is co-ordination, authentication and, in exceptional cases, control.”