Idle Thoughts of an Idle Fellow is a collection of humorous essays by Jerome K. Jerome. It was the author's second published book and it helped establish him as a leading English humorist. While widely considered one of Jerome's better works, and in spite of using the same style as Three Men in a Boat, it was never as popular as the latter.

A second "Idle Thoughts" book, The Second Thoughts of An Idle Fellow, was published in 1898. The essays had previously appeared in Home Chimes, the same magazine that later serialised Jerome's Three Men in a Boat.

The book consists of 14 independent articles arranged by themes: ON BEING IDLE. ON BEING IN LOVE. ON BEING IN THE BLUES. ON BEING HARD UP. ON VANITY AND VANITIES. ON GETTING ON IN THE WORLD. ON THE WEATHER. ON CATS AND DOGS. ON BEING SHY. ON BABIES. ON EATING AND DRINKING. ON FURNISHED APARTMENTS. ON DRESS AND DEPORTMENT. ON MEMORY.