These are works on Angels, or angelology, and they have sub-divisions of good angels, bad angels, and specifically Satan.

Note that I am fully aware that (1) “angel” means messenger and that many times in Scripture the Hebrew and Greek word is translated “angel” or “messenger” purely from the context, and I have not addressed this human side of the concept at all here. Few works address men as “messengers” in itself, except as ministers of the gospel. So those works would be in “ministry”.

(2) “Angel” is a poor description and concept really. It means messenger, and within the studies, works, and understanding of most Christian theologians the concept is “made in stone” a good spiritual being serving God. There may be “angels” (spiritual servants of God) that are not just messengers, but which constantly praise God, or do some other bidding of God, and therefore the concept of angel (messenger between God and man) would not correctly fit for them. None-the-less most writers will use this generic term “angel” for these spiritual beings, so I am including them here also.