HarperCollins Publishers L.L.C is one of the world's largest publishing companies and is one of the Big Five English-language publishing companies. It is a subsidiary of News Corporation. They have published all existing books in the Warriors series.
HarperAudio is an imprint of their parent company HarperCollins, and have released all existing English-language Warriors audiobooks. They employ audiobook narrators, who are a group of people that have worked to record the Warriors series in audio format. There are three narrators for the English language, including MacLeod Andrews and Kathleen McInerney.
Tokyopop is an American distributor, licensor, and publisher of anime, manga, manhwa, and Western manga-style works. Alongside HarperCollins, they have released all existing English language Warriors manga.
Working Partners was involved with the concept development of Warriors. They are a company that develops book ideas, brings then to a draftable stage, and then pitches them to publishers. HarperCollins picked up Warriors from them, and recruited Kate Cary and Cherith Baldry, along with Victoria Holmes, the original story drafter, to make a 6 book series. From there they continued to work on the Warriors series with Vicky, and later Clarissa Hutton.