The Oxford Dictionary of the Christian Church, 4th ed. (Online) by Andrew Louth (editor) 6,000 cross-referenced A-Z entries from theology; churches and denominations; patristic scholarship; and the bible; to the church calendar and its organisation; popes; archbishops; saints; and mystics. Online available. Newly updated in 2022.

The Oxford Handbook of Early Christian Studies by Susan Ashbrook Harvey (Editor); David Hunter (Editor) Provides an introduction to the academic study of early Christianity (c. 100-600 AD) and examines the vast geographical area impacted by the early church, in Western and Eastern late antiquity. It is thematically arranged to encompass history, literature, thought, practices, and material culture.

The Oxford Handbook of Medieval Christianity (Online) by John H. Arnold (Editor) An overview of the beliefs, practices, and institutions of the Christian Church between 400 and 1500 CE. The Handbook is arranged thematically, and focuses on an analytical approach.

The Oxford Dictionary of the Middle Ages (4 Volume Set)-Online by Robert E. Bjork Accessible online. Each entry contains a brief bibliography. A balanced coverage of both the whole geographical extent of the European Middle Ages and sixteen major topics centrally important to the study of the period.

The Oxford Encyclopedia of the Reformation (Online) by Hans J. Hillerbrand (Editor) Sets the issues of theology and ecclesiology within the broader context of the social and intellectual history of the Reformation. A bit dated at some points.

The Oxford Handbook of Christianity in Asia by Felix Wilfred (Editor) Explores the world of Asian Christianity and its manifold expressions, including worship, theology, spirituality, inter-religious relations, interventions in society, and mission.

The Oxford Handbook of Latin American Christianity (Online) by David Thomas Orique (Editor); Susan Fitzpatrick-Behrens (Editor); Virginia Garrard (Editor) Examines Latin American Christianity in all of its manifestations from the colonial to the contemporary period.

Routledge Companion to Christianity in Africa by Elias Kifon Bongmba (Editor) Offers a multi-disciplinary analysis of the Christian tradition across the African continent. Traces the introduction of Christianity in Africa, as well as its growth, developments, and effects, including the lived experience of African Christians.

The Oxford Encyclopaedia of South Asian Christianity (Online) by Roger E. Hedlund This encyclopaedia documents the historic presence and contributions of Christianity in India and its neighbouring South Asian countries (Bangladesh, Bhutan, Nepal, Pakistan, Sri Lanka, and the Maldives). In addition, the volume includes entries on Afghanistan and Myanmar and on the global South Asian diaspora.