Everyone knows the famous expression "Three's a crowd!”—but that sentiment doesn't ring true when it comes to audiobooks. Over the past decade or so, the popularity of trilogies has exploded, and a few stories that are part of trilogies have become some of the best-selling books of all time. The Hunger Games trilogy from Suzanne Collins and the Twilight trilogy by Stephanie Meyers are two of the most successful examples. Or consider Fifty Shades of Grey, the first installment of E.L. James's Fifty Shades trilogy, which was the best-selling book of the last decade.

A trilogy, by definition, is a group of three related works. Audiobooks in trilogies are three separate installments that tell one overarching story. While many authors have their whole trilogies planned out ahead of time, some choose to write them as they go along. Other authors might hesitate to call a book the first in a trilogy, because they are not sure how many books they want to write featuring that story. For example, Douglas Adams famously wrote what was called the Hitchhiker's Guide to the Galaxy trilogy but then continued on, and added two more books to the series. So now the series is jokingly referred to as "a trilogy in five parts."

And sometimes, an author might write a trilogy, but then also write other works featuring the same characters or the same universe. To use Suzanne Collins as an example again, her Hunger Games trilogy was considered completed for many years; but this year, she released a prequel about one of the characters called The Ballad of Songbirds and Snakes.

The word "series" is usually used to describe three or more things. So while three audiobooks doesn't sound like a lot—especially considered against prolific series authors such as J.D. Robb, who has more than 50 listens in her Eve Dallas series!—a trilogy does indeed qualify as a series. And while there certainly seem to be more trilogies in genre fiction such as sci-fi and mystery, wonderful trilogies are found in just about every genre.

What are the best trilogies of all time? With thousands of amazing trilogies out there, it's hard to narrow it down. But we’ve compiled some audiobook trilogies that represent the best of the best—and don’t worry about spoilers; we’ve only described the first of the series in each entry.

MaddAddam
Shadow and Bone
City of Stairs
Dawn
Sea of Poppies
The Fifth Season: Booktrack Edition
The Three-Body Problem
Wolf Hall
Some Luck
The Fellowship of the Ring

Liberty Hardy is a Book Riot senior contributing editor and velocireader living in the great state of Maine with her trilogy of cats, Millay, Farrokh, and Zevon, who hate to read.