The Tale of Peter Rabbit was first commercially published in 1902 by Frederick Warne & Co. Beatrix Potter wrote and illustrated the story, which follows Peter's disobedient adventure in Mr. McGregor's garden.
The date can be confusing because Potter had the book privately printed in 1901 after several publishers rejected it. That small private edition was not the commercial trade publication normally meant by this question. Frederick Warne issued the first full-colour commercial edition in October 1902, bringing Peter Rabbit to a much wider audience.
Potter's compact format, vivid illustrations, and carefully controlled page design were unusual for the period. The book quickly became a success and helped launch a long publishing relationship between Potter and Warne. By December 1903, it had sold 50,000 copies, and it has remained in print for more than a century.