Additional rights beyond primary book publication - like translation, film, audio, and merchandise - that can each be sold separately for additional income.
Subsidiary rights (often called 'sub rights') are the secondary rights that branch off from a book's primary publication right. When you write a book, you don't just own 'the right to publish it.' You own a bundle of distinct rights: the right to translate it, adapt it for film, produce an audiobook, serialize it in a magazine, create merchandise, and more. Each of these can be licensed or sold independently, often to different buyers. In traditional publishing deals, the negotiation over which sub rights the publisher controls versus which the author retains is one of the most consequential parts of the contract.
Subsidiary rights can generate far more money than the original book deal. A novel that earns a modest advance might land a six-figure film option or get translated into 30 languages. Understanding what rights you're signing away in a publishing contract is crucial. Many authors and agents fight to retain certain sub rights specifically because they represent long-term earning potential.
Tolkien sold the film rights in 1969 for just 10,000 pounds, not foreseeing the eventual Peter Jackson trilogy. A cautionary tale about undervaluing sub rights.
The film/TV rights turned a bestselling novel into an Emmy-winning HBO series starring Nicole Kidman and Reese Witherspoon, dramatically boosting book sales in return.
Make a list of every subsidiary right your current work-in-progress could generate. Translation? Audiobook? Film? Graphic novel adaptation? Video game? Now rank them by which you'd most want to retain if a publisher offered you a deal. Research what a typical split looks like for your top priority.