The Oxford Bible Commentary by 
The Concise Oxford Dictionary of the Christian Church by Below are key reference books that provide a general overview of a topic or help identify synonyms, related terms, or basic data. These sources often include references and lists of further readings.
The Anchor Bible Dictionary by 
The Oxford Companion to the Bible by 
Encyclopedia of Early Christianity by 
The Oxford Companion to Christian Thought by 
Brill's New Pauly by 
The Oxford Dictionary of the Christian Church by 
Encyclopedia of the Early Church by 