Technically, an epilogue is a book's ending, but it does more than just finish up the plot elements. However, the epilogue shouldn't take the place of the book's climax; it should add to it. Epilogues can weigh down a story if the author doesn't know why he's writing it. A strong epilogue can foreshadow a future novel, help readers understand the aftermath of the book's climax or add realism to the tale.
A writer can choose from a number of epilogue styles, and which he chooses depends upon the information he hopes to convey. Perhaps the author wants the reader to know how the climax affected future events or relationships. For example, if society as it's presented breaks down or a major character dies, the epilogue shows how the remaining characters and society cope: Suzanne Collins's "Mockingjay" does this by showing what happens to main characters Katniss and Peeta in their lives after the arena. An epilogue can also give the book's audience an overall view of the world inhabited by the characters after the story ends. Many sweeping sagas do this. They wrap up by suggesting family ties, revealing who marries whom or when major characters pass away. Finally, an epilogue can give the author license to try a different style of writing, such as leaving the reader with a few words of poetry or having a character make a speech.
Climaxes can leave readers in the lurch, particularly if they are traumatic. If a book's main character dies, an author can use the epilogue to explain to the audience how the remaining characters have adjusted. This type of ending works well if the author has told the story from two or more points of view throughout the book. Veronica Roth uses this technique in the novel, "Allegiant." By telling the story from more than one point of view, the reader can empathize with multiple characters and accepts that someone other than the primary protagonist will have the last word.
Although epilogues give the writer some creative options, writers might want to avoid certain techniques. For example, most writers don't start a story in first person and then switch to third person. However, even this can work if approached skillfully. For example, the change in voice can come in the form of a letter, diary entry or newspaper account. This technique is called epistolary fiction; Stephen King told his story "Carrie" through this type of literary device. As with telling the story from multiple points of view, this technique should make its appearance from the beginning of the book to be most successful. It works because the reader has grown accustomed to the voice presented and won't feel jarred out of the story if the author uses the technique in the epilogue.
In a Writer's Digest article, author Nancy Kress tells writers to construct an epilogue that is proportionate to the story. In other words, if the story is short, then a short epilogue is in order. Kress thinks a two-paragraph epilogue would be appropriate. For longer works like novels, the writer can devote several pages or sections to the epilogue. If the author uses the epilogue to point to events that may occur in a sequel, those revelations should take the form of hints, rather than summaries. The reader shouldn't get the feeling that the writer has started a new book in the final paragraphs or pages of a work.
Yes, many readers love happy endings and the good feelings they impart. However, an epilogue shouldn't undo the story's essential conflict, particularly if the story isn't a particularly happy one. The best epilogues connect with the themes and retains the tone that the author introduced throughout the work. Suzanne Collins's "Mockingjay," part of the "Hunger Games" series, provides an example of this. By the book's conclusion, the Hunger Games have ended and the main characters have found some relative happiness. However, the epilogue makes it clear that the awful traumas they experienced throughout the three books in the series will affect them for the rest of their lives.