How can I stop the Books App from making another copy of my audiobooks into its library?

You're very welcome! I'm glad you got it worked out in spite of my not-so-accurate steps. ;)

Great job getting this accomplished! ... and for providing your final solution. I'm sure it will help others who may come across the same issue.

The audiobook files are stored here:

There's no way around it. So after importing your audiobook files into the Books library delete the originals from the hard drive. When you're done with the book you can delete it from the library and it will end up in a folder in the Trash bin where you can recover them and store on an external drive if desired. OR, if they were originally on an external drive just leave them there.

In any case we're forced to store the books on our internal boot drive. Only have 59 GB in my library currently but have removed 268 GB of books after having listened to them and stored them on an external drive.

I've tried moving the Audiobook folder to an external drive and putting a hard link and then an alias in its place with no success. If you find a way to store them externally come back and let us know.

Unfortunately, AFAIK there isn't a built-in option in the Books app to stop it from copying files to its library, like the Music app. However, you can use the following workaround to save some storage space:

1. Move your audiobooks to a designated folder (e.g., "Audiobooks") in a location of your choice.

2. Create an alias (also known as a shortcut) for each of your audiobook files:

a. Click on the audiobook file.

b. Press the following keys: "Command + L" (⌘L) to create an alias for the file.

c. Repeat this process for all your audiobook files within the folder.

3. Import your aliases into the Books app:

a. Open the Books app.

b. Go to "File" in the top menu, and click on "Add to Library" (or press "Command + O" on your keyboard).

c. Locate and select the alias files in the folder you created earlier, and click on "Open" to add them to the Books app.

By doing this, the Books app will reference the original files through the created aliases without duplicating the files in its library.

Please note that you need to keep the original files in the designated folder to avoid breaking the links to the aliases. If you move or delete the original files, the aliases will no longer work in the Books app.

A older thread, but just for the record...

Unfortunately, this alias trick doesn't work. It copies the file linked in the alias to the library's storage location, not just the alias. So you don't save any space by putting the source files on an external drive and using aliases.

Come on Apple, fix this huge missing feature.