The Railway Series (1945-2011) is a series of British books by the Rev. Wilbert Awdry (Books 1-26) and Christopher Awdry (Books 27-42).

Unless otherwise said on this page, the technical notes come from actual notes laid out by Wilbert Awdry when he was developing the characters and setting for his stories; these notes are cited in his publication The Island of Sodor: Its People, History, and Railways.^[1]

The North Western Railway (NWR) is the main standard gauge rail network on the Island of Sodor. The railway's motto is "Nil Unquam Simile", which is Latin for "There's nothing quite like it". From nationalisation on January 1, 1948 until it privatised, the railway was the North Western Region of British Railways (BR). From 1925 onwards, it has been managed by three Fat Controllers.

“Please tell everyone that whatever happens elsewhere, Steam will still be at work here. We shall be glad to welcome all who want to see and travel behind, real engines.”

― Sir Charles Topham Hatt II/The Fat Controller, Little Western, Enterprising Engines

The Skarloey Railway (SR) is a 2'3" narrow gauge railway, which runs from the North Western Railway's station Crovan's Gate to Skarloey. Beyond Skarloey, the line continues to a former slate quarry, now used as ammunition dumps. The railway is owned by Sir Handel Brown, who serves as its chairman and is run by Mr. Roger Sam, son of the previous controller, Mr. Peter Sam. The locomotives are all based on their Talyllyn Railway counterparts.

The Culdee Fell Railway (CFR) is Sodor's only rack railway. It climbs to the top of Sodor's highest mountain, which shares the railway's name. It is based on the Snowdon Mountain Railway in North Wales, was opened in 1900 and for many years was operated under the direction of Mr. Walter Richards, the General Manager. The railway was only featured in Mountain Engines. The locomotives on the line are all 0-4-2RTs.

The Arlesdale Railway is Sodor's smallest railway. It is based on the Ravenglass & Eskdale Railway in Cumbria. The railway is run by Fergus Duncan (The Small Controller). Its five engines appear in the books. The diesel locomotives are mentioned in the companion books: Sigrid of Arlesdale, Blister I and Blister II.

Various engines from British Railways (BR; also known as "the Other Railway"), and some from preserved/private railways and museums have visited the North Western Railway, both on regular trains to-and-from the Mainland, for special events, or under a lease agreement.

• Sir Charles Topham Hatt II, better known as the Fat Controller, is the manager of the North Western Railway. He makes sure everything is running well and right on time, without confusion and delay. His son, Charles, succeeded him in 1954, and his grandson, Stephen, became the third controller in 1984. His son, Richard, would be the next Fat Controller.
• Sir Handel Brown is the manager of the Skarloey Railway. He often had other business to attend to and was never seen in the books.
• Peter Sam, known as the Thin Controller, is the vice president of the Skarloey Railway. He succeeded his father, Mr. Robert Sam in 1951 and was hired by the new owner, Sir Handel Lloyd Brown. Like his father, he spent his entire working life on the Skarloey Railway.
• Fergus Duncan, known as the Small Controller, is the manager of the Arlesdale Railway. Despite being known as by his nickname, he is taller than both the Fat Controller and the Thin Controller.
• The Fat and Thin Clergymen are two clergymen with a strong interest in the railways on Sodor. The Thin Clergyman is an author and is strongly hinted to be the Rev. W. Awdry. The Fat Clergyman, who likes taking pictures, is implied to be the Rev. Wilbert Awdry's real-life friend, the Rev. Teddy Boston.