Thomas & Friends (originally known as Thomas the Tank Engine & Friends and later Thomas & Friends: Big World! Big Adventures!) is a British children's television series that aired across 24 series from 1984 to 2021. Based on The Railway Series books by Rev. W. Awdry and his son Christopher, the series was developed for television by Britt Allcroft. The series follows the adventures of Thomas, an anthropomorphised blue steam locomotive on the fictional North Western Railway on the Island of Sodor, and many other anthropomorphised locomotives on the North Western Railway, including Edward, Henry, Gordon, James, Percy, and Toby. They work for Sir Topham Hatt, primarily known as the "Fat Controller".

In the United States, it was first broadcast along with the spin-off series Shining Time Station on PBS' PTV Park block in 1989.

The rights to the series are currently owned by HIT Entertainment (a subsidiary of Mattel), which acquired Gullane Entertainment in July 2002.

A new 2D-animated series, Thomas & Friends: All Engines Go, premiered on 13 September 2021 on Cartoon Network.