Postings for a couple of books on my bookshelf don't have back cover descriptions of the plot of the book. Is there a way to add this to the posted books?

Members can add to the Wiki portion of the listing, but IIRC not the actual book information.  Check with a Book Data Editing volunteer.

If you go under More Options  on the book's page, there's an edit book data button.  Go there and either type in the book description or copy/paste it from somewhere. It's helpful to fill in whatever else you can.  You can even upload photos there too if it's missing a cover. Then hit submit.  A data editor will review it and make changes.  If there's a problem with your submission they will PM to let you know.  If there isn't than you won't get a response, you'll just see the change. 

What Mary said     And if ever there isn't a good description on the back of your book, often you can find one online.  We go for plot/contents descriptions rather than reviews.  Publisher's blurbs are good, too.  No physical descriptions  ("hardcover" or "no dust cover).

Awesome Mary, I'm going to try it soon too!

When I use the "Data Edit" process as Mary describes, in the reason for "data edit", I'll put something like "add book description from Amazon" (or whatever source I get the information from).  I figure that makes it easier for the Data Edit Team to verify the information and approve my changes sooner.

The approvers most definitely read the notes, and the extra information usually does prove useful to us, and can save us lots of time, which is especially helpful when there are hundreds of submitted edits awaiting approval!   The more information added in an edit, the better!   I love the members who help out by submitting data edits. 

Often you can find the descriptions on the author's page and copy and paste it right into the field on the Edit screen, rather than having to type the whole thing from the back of the book.

Amazon is a great source, as Laura mentioned as is www.fantasticfiction.co.uk

and www.worldcat.org

Thanks for the hint on saying where you got the info for the book description.  I almost always take it from the book jacket, but never thought of saying so.  Pat

Also I noticed a lot of people put reviews in the book description. You want a generic book descripton not a review.  I also try to add as many genres as I can to help it pop up on more searches. 

I wish that field was Synopsis rather than Description.  Wouldn't be so confusing. 

Adding genre helps us tremendously!   Something I just recently learned - the Homeschool checkmark and the line of genre  Nonfiction >> Education >> Homeschooling are linked; if you put one, you get the other. 

So if you want to mark a work of FICTION as suitable for homeschooling, please just add the homeschool  TAG.