Being a professional genealogist requires specialized training. It also requires acquiring a pretty robust library of books specific to genealogy. I really didn't expect the amount of genealogy specific books that existed and that I would need to have on hand. Several of these books are "must-haves" for any genealogist. Those would include the most current editions of all of these: Evidence Explained: Citing History Sources from Artifacts to Cyberspace by Elizabeth Shown Mills, The Chicago Manual of Style, Mastering Genealogical Proof by Thomas W. Jones, The Family Tree Guide to DNA Testing and Genetic Genealogy by Blaine Bettinger, and, of course, Genealogy Standards from the Board for Certification of Genealogists. Along my journey of going from a hobbyist to a professional, I have acquired all of these books and then some!
Other books that have proven to be quite useful to me are those that are more specialized. Nicknames: Past and Present by Christine Rose, Death Certificates and Archaic Medical Terms by Helen V. Smith, Reading Early American Handwriting by Kip Sperry, and Numbering Your Genealogy by Joan Ferris Curran, Madilyn Coen Crane, and John H. Wray are invaluable references as I analyze documents and write research reports. (Reading that old handwriting is definitely a whole new skill AND I need A LOT of practice on that one!) There are also specialized books that focus on genealogically important records, such as land (Land & Property Research in the United States by E. Wade Hone), legal (Genealogy and the Law: A Guide to Legal Sources for the Family Historian by Kay Haviland Freilich and William B. Freilich), and church (How to Find Your Family History in U.S. Church Records: A Genealogist's Guide with Specific Resources for Major Christian Denominations before 1900 by Sunny Jane Morton and Harold A. Henderson CG©).
Of course there are the books that focus on specific areas of my research that are oh-so helpful as well. These books will vary from genealogist to genealogist, as each genealogist has different specialties and target areas. The books now in my library that have been of useful for me are: Elsa and Anna in America-Dutch New Amsterdam by Thomas P. Miller (for looking for my mother's Fulkerson ancestors), Tracing Your Ancestors from 1066 to 1837: A Guide for Family Historians by Jonathan Oates (for looking for my father's Goolsby ancestors and my husband's Chapmans), Tracing You Irish Ancestors by John Grenham (for looking for my husband's Thompsons), and The Family Tree German Genealogy Guide: How to Trace Your Germanic Ancestry in Europe by James M. Beidler (for looking for so many of our ancestors!).
Additionally, there are other must-have books for professional genealogists about running a business. The gold standard of these books is Professional Genealogy: Preparation, Practice & Standards edited by Elizabeth Shown Mills (I actually have both editions!). This is truly the text book of what you need to know to be a professional genealogist. In addition, I use the app Evernote in my work, so I have Kerry Scott's How to Use Evernote for Genealogy: A Step-by-Step Guide to Organize Your Research and Boost Your Genealogical Productivity. And since I love to organize things, I have Organize Your Genealogy: Strategies and Solutions for Every Researcher by Drew Smith!
On top of all of these books in all of these categories (and many others I have not included here!), there are all of the journals, magazines, and newsletters from all of the professional organizations (3), historical societies (11), and lineage/family societies that I belong to (2 with 3 more in progress). Whew! That's a lot! And since my husband and I already had a "book problem" before I became a professional, I REALLY needed to figure out a solve for my genealogy books and periodicals. The solution (drum roll, please) -- two rolling carts from Ikea. The cart is the RÅSKOG (in case you were wondering what its unique Ikea name is). The cart is quite sturdy and not that hard to put together.
Of course in 2021, there are also myriad digital sources that genealogists utilize for research. My bookmark bar in Google has a genealogy folder with at least 19 sub folders and who knows how many links! With that said, I have found that having many of these actual, old-school books on hand has proven immensely helpful as I work on research and writing. And I know that there are more books that I need to acquire (Black's Law Dictionary to name but one!). I just hope two carts will be enough!