Many subjects have multiple reference sources available, by different editors and publishers, varying by date, length, and, in some measure, viewpoint. For example, research on biblical interpretation is served by a variety of reference works, covering a variety of approaches to and historical contexts of biblical interpretation.
Dictionary of Biblical Interpretation by 
Dictionary of Biblical Interpretation, 2 vols. by 
Dictionary of Biblical Criticism and Interpretation by 
Dictionary for Theological Interpretation of the Bible by 
Dictionary of Major Biblical Interpreters by 
Encyclopedia of the Bible and its Reception by 
Encyclopedia of Ancient Christianity by Encyclopedia of Ancient Christianity (online) by 
Wiley Blackwell Companion to Patristics by 
Encyclopedia of Early Christianity, 2 vols. by 
Dictionary of the Later New Testament and Its Developments by 
Dictionary of the Later New Testament and Its Developments (online) by 
Early Christian World, 2 vols. by 
Dictionary of Early Christian Literature, 2 vols. by 
Trinitas by 
Verbum Caro: An Encyclopedia on Jesus, the Christ by 
Veni Creator Spiritus by 
Ecclesia by 
Theotokos: An Encyclopedia of the Blessed Virgin Mary by 
Creeds and Confessions of Faith in the Christian Tradition, 4 vols. by Several different reference sources are also available on Judaism, for example. Though the most recent and extensive scholarly resources on your subject are usually preferable to older and shorter/briefer resources, others may also be useful for you, depending on your subject and the nature of your research. In any case, consulting all that may be helpful is usually advisable, rather than limiting your reference work to one or two sources.
New Encyclopedia of Judaism by 
Encyclopedia of Judaism by 
Concise Encyclopedia of Judaism by 
Eerdmans Dictionary of Early Judaism by 
Dictionary of Judaism in the Biblical Period: 450 B.C.E. to 600 C.E., 2 vols. by 
