By David Kudler on The Book Designer:
One of the great advantages of ebooks over their paper-and-ink friends is that it’s relatively easy to create a compilation or box set. This is true whether you are pulling together:
A collection of your own articles or stories
An anthology of stories/articles by a number of authors
A single-volume omnibus of your 21-title epic fantasy series
A giveaway ebook featuring your own work and one or more other author’s, allowing you to introduce your readers to each other’s writing
Pulling together a volume like that for print can get unwieldy quickly, since at a certain point the length of your book makes it uneconomical to publish. [i]
Doing so for digital distribution, on the other hand, has no real upper limit. I’ve released ebooks containing over a million words. The only constraints have to do not with creating such a book, but with marketing it — do you really want to sell your entire life’s work in a single volume for $9.99? Maybe you do. Maybe you don’t.
But the point is, if you want to you can.
There are basically two ways to create a compilation ebook:
Combining the source files
Combining the ebook files