Most general reference encyclopedias in religion have articles on Advent, and links to several are provided below. Pay special attention to bibliographies in the encyclopedia entries, which include references to the key works on a topic. Two kinds of online reference materials are included here. Listed to the left are topic or overview pages for Advent and Christmas, with some dictionary entries. Listed to the right are the more traditional reference works such as multi-volume encyclopedias, which are often the online edition of a work first produced in print.
For more reference resources about Advent, check out this link. This search includes online and physical resources.