Church history or ecclesiastical history as an academic discipline studies the history of Christianity and the way the Christian Church has developed since its inception.

Henry Melvill Gwatkin defined church history as "the spiritual side of the history of civilized people ever since our Master's coming". A. M. Renwick, however, defines it as an account of the Church's success and failure in carrying out Christ's Great Commission. Renwick suggests a fourfold division of church history into missionary activity, church organization, doctrine and "the effect on human life".

Church history is often, but not always, studied from a Christian perspective. Writers from different Christian traditions will often highlight people and events particularly relevant to their own denominational history. Catholic and Orthodox writers often highlight the achievements of the ecumenical councils, while evangelical historians may focus on the Protestant Reformation and the Great Awakenings.