The companies may provide exclusive distribution rights, or act as a wholesaler or warehouser of publisher's titles.
Many of the companies distribute other products, and some also sell directly to the public.
Book distributors offer a consolidated list of publisher's titles, such that bookstores can purchase from a wider range of publishers than if they had to open separate accounts with each publisher, who often require a minimum order that the bookstore cannot meet.
Most small or independent publishers have relationships with a distributor, including self-published authors, who often use services like Amazon.com to sell to the public.
The large publishing companies, including the "Big Five" (Penguin Random House, Hachette, Macmillan, HarperCollins and Simon & Schuster), act as distributors for the numerous imprints they have acquired over the years.