My questions are: How much do you assume readers know from the previous book(s)? How much do you have to reintroduce characters and their relationships? How much of what happened before do you need to bring out? When the characters are not REALLY new, but continuing from the previous story, can you introduce a few more of them in the first chapter? It seems strange to ignore them when I know that they're right there, living next door so to speak.

This is a little more important to me in Book Three because I've also got to explain the events that took place in the time that elapsed between books two and three (about two years). So I don't want to have to do a lot of re-introduction of the characters, too.

There is a good sized prologue at the beginning which I imagine chronicles all that has gone before in the other two books, in a nutshell, so to speak.

That could very well be the right solution, here. Thank you.

Now I have to dig out a book that used that, if I have one, just to have a look at how it was handled.

If nothing else, it's a first step towards writing the synopsis. Although the prologue is way too long for that purpose.

I've found this a chronic problem. Sequels, especially in the lengthier series, sometimes seem utterly dependent on "what has gone before." Not just information, but actual plot developments, too. Even the tone of the story shifts a lot.

Try to make it just sufficient enough to get a handle on the story rather than a regurgitation of all that went on in the past. This should be relatively easy if your previous books are self-contained as you mentioned above.

Every book needs to be it's own story. Which means each book is a different book.

That sounds simple, but I think it is important to realize that if you end a story with chapter eighteen, then chapter one of book two can not be just a chapter nineteen. I think you need to focus on what story (beginning middle end) you want to tell. What theme you want to use, and where it is you should begin.

Even in book one, things should have happened before the story takes place. So approach book two the same way you did book one.

The past is prologue. No matter if you use a prologue to share information or just memories when, and if, they seem important.

No story, if it is going to be believable, realistic, engaging, etc, happens in a vacuum. The characters need to seem to have existed before the story starts or they won't seem strong enough. The setting needs to be lived in as well, and the plot has to have been generated by things that have happened before the story starts.

So when you start any story, you have to provide some background, and I get the impression that one of the best ways to do that is to sift it gently into the story as it unfolds, instead of lumping it all into one big explanation.

That should work whether the story is the first of a series, the middle book, or the final book.

Prologues are another way to deal with the problem, though, and they are used for stand-alone novels as well as for later books in series. I'm one of those readers who tends to skip prologues, though, unless I still want MORE when I've finished the book, and the prologue is the only thing left for me to read.

So, I'm going re-read those. I remember really liking both of those trilogies anyway.

I'm currently reading near the end of Robin Hobbs's Assassin/Tawny Man saga, and really find it disruptive when she recaps backstory from previous books. I understand the concerns about readers jumping in at book 5 of 6 or something, but for the stalwarts who plow through from the beginning, relegating that kind of stuff to footnotes and appendices would be better.

I knew the story so well that the first time I saw the movies I spent about half the time saying "They skipped that" or "That's not right. It wasn't that way in the book".

We write a series of books numbered 1, 2, 3, etc, and what do they do? Start with book four.

So to make it easy for them, we write prologues -- which, more often than not, they skip. (Why? Because nobody likes infodumps and 'prologue' is really just a euphemism for 'infodump at the beginning'. The trick with the prologue is to entice the reader to read it; not easy.)

I think the best answer is to lace all they need to know into each book (story), because if we don't -- if they don't understand the story either because they didn't read the books in the right order, or they skipped the prologues -- we'll never know. We'll only know that sales were disappointing. They won't tell us they didn't buy the other books in the series because they didn't understand book four, they'll just buy something else.

Yes, that's not easy. It means, perhaps, introducing a new character for each book, one who needs stuff explained. Or, as in Harry Potter, it means having MC remember experiences (like how he got the scar) so we know his motivation (and in Harry's case it felt authentic, for one would indeed relive such an experience when the memory is provoked).

The initiating post mentions using the prologue to explain events that happened between books. I fear that's a mistake: surely, significant events ought to be in one book or another? Missing them out risks making the reader feel short-changed, perhaps?

I wasn't clear enough about that, I think. The events between books are, in fact, between books because they're BORING. There are some socio/economic/political shifts that take place over the course of a couple of years. Not having to put the reader to sleep with that is one reason for the gap. My MC will be sort of on the edge of these changes, but not deeply involved until later. Other than that, a couple of secondary characters would get married during the gap and one child would have been born just before Book Three opens.