The blurb (in the UK) is the bit on the back cover of a book, or sometimes the jacketflap if your book is fancy enough to have a jacket, that says how wonderful it is. The blurb tells prospective readers a bit about the book and its job is to entice them into buying/reading the book, so it has to work hard, and be just right - like Baby Bear's porridge. In fact, the Baby Bear's Porridge model of writing is the key to the whole thing. Your book must be not too long and not too short, not too experimental and not to too boring... it must be 'just right' in all regards. The problem is, 'just right' depends on which bear is eating the porridge. Writing - and publishing - is the art of assessing the bear as it approaches, and plonking the right bowl of porridge on the table. But I digress.
The blurb must appeal to the target reader, so a literary novel will usually have a serious, measured blurb that bigs up the themes and intellectual context of the book:
Anna Karenin is a tale of love, anguish and despair set against the backdrop of the constraints of nineteenth-century Russian society as it waltzes inexorably towards disaster. Stifled in her marriage and bored by all her restricted life has to offer, Anna forms a passionate and ultimately tragic liaison with Count Vronsky - but her temporary fulfilment comes at the cost of ostracism, the loss of her children and everything dear to her.
A mass-market or genre novel will have a shorter blurb that plays to what the reader is expecting, and bigs up the plot and character stereotypes. It may overdose on rhetorical questions in the hope of creating an aura of suspense and excitement. If Anna Karenin were marketed as a romantic novel, it might have a blurb like this:
Bored by her adequate but dull husband, Anna is bowled over by the handsome, dangerous Count Vronsky. Throwing caution to the winds, she embarks on a whirlwind affair that brings the passion and adventure she craves. But how long can Anna live under the condemning glare of Russian society? Will love conquer all, or will the price be too high for the couple?
For a children's book, the blurb may be designed to appeal to gate-keepers (parents, teachers, librarians) rather than children, depending on the title. If it is to appeal to children, it will be short and may be humorous. You should have the chance to write, or at least approve, the blurb.
The blurb might include a 'puff' - a quote from another writer, a reviewer or a celebrity saying how great your book is. You or the publisher might ask a chosen more-famous-than-you person to read an advance copy and give you a puff. If the book is reprinted, the publisher might take choice quotes from reviews. If you're given or come across a comment you want the publishers to use, pass it on. (Actually, this is a matter of do as I say and not as I do. Personally, I don't pass on comments which were made off the record - in private conversation or emails. This is probably very stupid, and means I've missed out on puffs from some very senior figures, but it seems to me that it's dishonest, or at best disingenuous. Make your own choices.)
The blurb might include a paragraph of author biog:
Leo Tolstoy is an exciting new voice from Moscow. His writing is incisive and precise, giving a devastating critique of aristocratic Russian life. Anna Karenin is his first novel.
If the blurb has a biographical element, you should certainly have control of this. If the publishers use the last biog you sent them, it may well be out of date. If you filled in an author-info sheet, this will probably be used as the basis of the blurb (and catalogue copy), so bear that in mind when you fill in the sheet.
The publishers will want to mention your previous books, any qualifications or relevant experience that excuse your having written the book (so you've been a polar explorer if your novel is set in the Arctic, or you are a surgeon if your book is a neurosurgery text book). They will want to mention any awards or shortlistings as long as they are important enough. They won't want to mention that you won the short story competition in the Shepreth Evening News or won the Gower Beach award for a first poem. (Don't look for entry forms, these don't exist.) They certainly don't want to mention that you self-published your first six novels (unless these then became mainstream successes). If they can't think of anything else to say they will say you are an exciting new voice and this is your first novel, or some such other generic gumph. They want to make you sound interesting. If you are not interesting, that makes the job harder. So try to live an interesting life.
I hate writing blurbs. Summing up the book you've spent months writing in one or two paragraphs is a horrid task. But it's better to tackle it than let an Emma who hasn't read the books write the blurb. (All publishing bints are called Emma if they are not called Rebecca; bint is not a pejorative term in StroppyAuthorSpeak - my daughters are widely know as Big Bint and Small Bint.) I've just looked at some of my blurbs (written by Emmas) and realise I need to follow my own advice - one switches from second to third person in a single sentence. Aaaargh. Grounds for a reprint? Or just time to crawl under a stone? I can write, people, honestly I can... Please buy the book - the writing inside is much better.
Thanks to Mary Hoffman for pointing at that what we call a puff in the UK is 'blurb' in the US. Does anyone know the American word for what we call the blurb, please?