The book tells the story of Horton the Elephant who one day, on the fifteenth of May in the Jungle of Nool to be precise, hears a small speck of dust talking to him. It turns out the speck of dust is actually a tiny planet, home to a city called "Who-ville", inhabited by microscopic-sized inhabitants known as Whos.

The Whos ask Horton (who, though he cannot see them, is able to hear them quite well due to his extraordinary hearing) to protect them from harm, to which Horton happily obliges, proclaiming throughout the book that "a person's a person, no matter how small". In doing so he is ridiculed and nearly murdered by the other animals, such as the Wickersham Brothers and the Sourpuss Jane Kangaroo, and the small kangaroo in her pouch, in the jungle for believing in something that they are unable to see or hear. Horton tells the Whos that they needed to make themselves heard to the other animals, lest they end up as part of "beezlenut stew", which they finally accomplish. The Who's finally make themselves heard by ensuring that all members of their society play their part. In the end it is the smallest Who of all, Jo-Jo, who provides the last volume lift to be heard, thus reinforcing the moral of "a person's a person no matter how small".

http://www.answers.com/topic/horton-hears-a-who

有人說，在美國如果你問最受兒童歡迎的作者是誰，無論是書店或圖書館人員都會告訴你是Dr. Seuss。Dr. Seuss使得閱讀和學習成為一種樂趣，他有超級豐富的想像力和特殊的畫風，沒有華麗的布景，沒有炫麗的色彩，但那似乎有旋律、有節奏的對白，使人讀後回味無窮。

Dr. Seuss本名Theodor Seuss Geisel，於1940年生於美國伊利諾州。自他1937年開始出版第一本書And to Think That I Saw it On Mulberry Street到1991年去逝，一共創作了48本兒童圖畫書。美國歷年兒童暢銷排行榜上的常勝軍，世界重要的兒童文學大獎，從來沒有缺過Dr. Seuss的名字，包括美國童話書最高榮譽凱迪克大獎、普立茲特殊貢獻獎等。在兒童文學和教育上都有劃時代的貢獻。

Dr. Seuss作品的風格常利用一些無意義或荒唐的事做為重要的出發點來從事創作，身邊看來不起眼的事，經過他的豐富的想像力，就會創作出一本與眾不同的童書。Dr. Seuss筆下的人物看起來有點怪怪的，但每個人物都有鮮明獨特又可愛的個性。看了Dr. Seuss的書會不知不覺的大聲朗讀起來，因為他的書充滿了節奏和韻律，念起來非常順口，可加深印象。