Classifying your book properly in order to reach libraries and bookstores is an important step that can only be done through a well-trained source.
It’s not something you can do by yourself and it is the best way to let libraries know you are serious about promoting your book to them.
If you are really serious about getting into libraries (which are buying a lot of ebooks and audible books now!) and big bookstores, this really is a MUST DO on your list.
OTOH, if you are doing short stories, novellas, and ebooks and don’t plan on approaching libraries or bookstores, don’t go to the extra expense. For example, my next two novellas won’t have this information. However, I will do it for my printed book that will include all four novellas in an omnibus.
I just got mine done for Wicked Wolves and here it is:

Here are some important terms to know:
The LCCN / PCN is optional and must be requested prior to your book being published. You request that through the Library of Congress. For small publishers and self-published authors, you can request a PCN (Preassigned Control Number) directly from the LoC for no charge here: https://www.loc.gov/publish/pcn/
I requested one AFTER my book was published (I didn’t know about this beforehand) and I was declined. That is okay as it is optional.
The CIP / PCIP (the latter is for self published books) is needed for librarians to easily classify your book into their system. Without it, a librarian will have to hand code your book into their system and this would decrease our chances of your book being considered.
I purchased mine through Five Rainbows and you can see it above. I’ll be putting this information on a page near the front of my book near the copyright data.
The MARC (MAchine Readable Catalog) is an online data file that includes everything in the PCIP plus some more stuff, in a specialized format that can be read by almost any online catalog system. It is inputted into the databases that librarians access to review possible books to purchase.
The package I bought from Five Rainbows included this. This all sounds really complicated, but it actually was pretty easy!

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