Humble Bundle and book publisher Harper Collins have teamed up for a new book bundle focusing on the beloved Discworld series of fantasy novels by late author Terry Pratchett. The aptly named Terry Pratchett’s Discworld Bundle includes up to 38 ebook editions of mainline Discworld novels, and like other Humble bundle deals, a portion of all sales goes to charity.

The bundle comes in multiple pricing tiers, and the more you pay the more books you get. For just $1, you get the first three Discworld novels: The Color of Magic, The Light Fantastic, and Equal Rites, all in ebook form. Pay at least $10, and you get the first nine novels in the series–including the three ebooks from the $1 tier, plus Mort, Sourcery, Wyrd Sisters, Pyramids, Guards! Guards!, and Eric.

If you pay $18, you get the full bundle, which includes all the ebooks from the previous tiers, plus 29 more. That’s 38 Discworld novels, which is almost the full series and equivalent to $401 for just $18. The only mainline Discworld titles not included in the bundle are book twenty-seven, The Last Hero, and the final two novels in the series, Raising Steam and The Shepherd’s Crown. You can check the full lineup of included ebooks on the bundle’s Humble store page. All books are delivered via Kobo.com, which requires a free account to access.

Discworld is often considered one of the best fantasy series of all time, acclaimed for its memorable characters and absurdist high-fantasy storylines that balance action and drama with Pratchett’s iconic sense of humor. However, between 41 mainline novels with intersecting storylines, plus numerous short stories, spinoffs, and even a collection of science books detailing how the universe of Discworld works, it can be daunting to get into. That makes this bundle all the more enticing since you can get the majority of the series for less than $20.

Humble donates a portion of all sales of the Terry Pratchett’s Discworld bundle to the Room to Read charity, which helps low-income students learn to read and develop other literacy skills. Customers can increase their pledge if they want to send more money to the organization, and can adjust their order’s revenue split between the charity, the book publisher Harper Collins, and Humble before checkout.

Humble’s Terry Pratchet’s Discworld Book Bundle is available through January 31.