Ecclesiology usually refers to the theological study of the Christian Church. However when the word was coined in England in the late 1830s, it was defined as the science of the building and decoration of church buildings and it is still, though rarely, used in this sense.

In its theological sense, ecclesiology deals with the church's origin, its relationship to Jesus, its role in salvation, its discipline, its destiny, and its leadership. Since different ecclesiologies give shape to very different institutions, the word may also refer to a particular church or denomination’s character, self-described or otherwise – hence phrases such as Roman Catholic ecclesiology, Lutheran ecclesiology, and ecumenical ecclesiology.

The roots of the word ecclesiology come from the Greek ἐκκλησίᾱ, ekklēsiā (Latin ecclesia) meaning "congregation, church"; and -λογία, -logia, meaning "words", "knowledge", or "logic", a combining term used in the names of sciences or bodies of knowledge.

Its first appearance in print, as ecclesialogy, was in the quarterly journal The British Critic in 1837, in an article written by an anonymous contributor who defined it thus: