[Note: this article has been edited since it was first posted to include new books on the topic.]
Some magickal practitioners focus on working with non-physical entities, whether these entities are described as elementals, faeries, ghosts, ancestors, angels, demons, saints, loa, intelligences, or deities. Different systems have different ways of categorizing and classifying — some are very strict about putting anything they consider to be “other” as automatically evil, while some practitioners might see those same entities as helpful or even as deities. Use your own judgement to determine if particular beings are friendly or antagonistic.
Personally I consider non-physical entities to be just as complex as physical creatures like humans. Whether a particular individual is friendly and helpful, or antagonistic and harmful, depends on circumstances and how I behave when I approach them. For example, my physical-world brother might be really nice to me but an absolute jerk to a stranger; just because a non-physical being is nice to me does not mean they will automatically be nice to everyone. The flip-side of that is also likely true: just because a spirit was nice to my neighbor does not automatically mean they will be nice with me. Keep your expectations realistic when beginning an interaction with an unknown spirit but definitely keep in mind what that spirit’s reputation might be with other practitioners too. And of course make sure you are well practiced in basic magickal cleansing and protection methods before you engage in any sort of spirit work. Don’t summon what you can’t send away again! (For books on magickal cleansing and protection, check out Pagan Booklist: Protection Magick.)
There are lots of books available that include sections on working with spirits as well as many books that are exclusively about this topic. Here are just a few that are more specifically about spirit work, to get you started. Once you find a book that you like be sure to check its bibliography as that can lead you to many other books that cover similar material to deepen your understanding.
And, as always, check with your local public library (ask about inter-library loans!) to borrow books if your budget is tight. If you want to purchase a specific book ask at local bookstores, or check stores online such as Amazon, or try my favourite multi-vendor used book search webpage, http://used.addall.com, to find the best place to purchase a book online.
Ghosts and Ancestral Spirits
Raven Grimassi, “Communing With The Ancestors”
Michelle Belanger, “Communicating With The Dead”
Martin Coleman, “Communing With The Spirits”
Christopher Penczak, “The Mighty Dead: Communing With the Ancestors of Witchcraft”
Mallorie Vaudoise, “Honoring Your Ancestors”
Phoenix LeFae, “What Is Remembered Lives”
Christian Day, “The Witches’ Book of the Dead” [Note: Christian Day has a not-so-great reputation among many in the Witch community due to his very public abusive behaviour towards those he disagrees with.]
More General Spirit Work
Jason Miller, “Consorting with Spirits: Your Guide to Working with Invisible Allies”
Ivo Dominguez, Jr., “Of Spirits: The Book of Rowan”
Ian Corrigan, “The Book of Summoning: A Grammary of Pagan Spirit-Art”
Yasmin Henkesh, “Trance Dancing With The Jinn”
Jan Fries, “Seidways”
Michael Osiris Snuffin, “Conjuring Spirits”
Vasilios & Lynn Wennergren, “Ars Vercanus: Advanced Magickal Techniques”
Aaron Leitch (editor), “Ritual Offerings”
Diana L. Paxson, “The Essential Guide to Possession, Depossession, & Divine Relationships”
Clare Fanger (editor), “Conjuring Spirits: Texts and Traditions of Medieval Ritual Magic”
Adam P. Forrest, “Liber Spirituum”
Joseph H. Peterson (editor), “Secrets of Solomon: A Witch’s Handbook from the Trial Records of the Venetian Inquisition”
Kenaz Filan & Raven Kaldera, “Drawing Down the Spirits,” and “Talking to the Spirits”
B. J. Swain, “Living Spirits: A Guide to Magic In A World of Spirits”
Hadean Press’ periodical “Conjure Codex: A Compendium of Invocation, Evocation and Conjuration” (currently 3 volumes published)
Hadean Press’ “Guides to the Underworld” particularly “Volume I: The Saints” for a more Christian folk-magick approach focussing on saints.
The Silver Elves, “An Elfin Book of Spirits: Evoking the Beneficient Powers of Faerie”
R. J. Stewart, “The Living World of Faery”
Ritual Magick (Goetia, Solomonic, Planetary etc.)
Aaron Leitch, “Secrets of the Magickal Grimoires”
Rufus Opus, “Seven Spheres” (planetary)
Frater Ashen Chassan, “Gateways Through Stone and Circle”
Jason Augustus Newcomb, “Conjuring the Goetia Spirits”
Konstantinos, “Summoning Spirits” (goetia)
Jake Stratton-Kent, “The True Grimoire”
Carroll “Poke” Runyon, “The Book of Solomon’s Magick”
Franz Bardon, “The Practice of Magical Evocation”
Steve Savedow, “The Magician’s Workbook”
Joseph C. Lisiewski, “Ceremonial Magic and the Power of Evocation,” and “Howlings From the Pit: A Practical Handbook of Medieval Magic, Goetia, & Theurgy”
Nick Farrell, “Helios Unbound: Pagan Theurgy to Connect to Your Higher Genius” is a pretty in-depth manual for performing the Abramelin operation of spirit contact but focussing on Pagan deities rather than Christian or Jewish ones.
Joseph H. Peterson, “Elucidation of Necromancy” is an in depth examination of the grimoire “Heptameron” with lots of hints about how modern practitioners can use it. For lots more about classic grimoires be sure to check out Peterson’s website at http://www.esotericarchives.com.