The stories, first published in 1902, are pourquoi stories, fantastic accounts of how various phenomena came about. A forerunner of these stories is "How Fear Came" in The Second Jungle Book (1895), in which Mowgli hears the story of how the tiger got his stripes.

The Just So Stories have a typical theme of a particular animal being modified from an original form to its current form by the acts of man, or some magical being. For example, the Whale has a tiny throat from a swallowed mariner who tied a raft in there to block the whale from swallowing others. The Camel has a hump given to him by a djinn as punishment for the camel refusing to work (the hump allows the camel to work longer between eating). The Leopard has spots painted on him by an Ethiopian (after the Ethiopian painted himself black). The Kangaroo gets its powerful hind legs, long tail, and hopping gait after being chased all day by a dingo, who was sent after the Kangaroo by a minor god whom the Kangaroo had asked to make him different from all other animals.

The original editions of Just So Stories were illustrated by Kipling.