The Portmadoc, Beddgelert and South Snowdon Railway (PB&SSR) was a 1 ft 11+1⁄2 in narrow gauge railway intended to connect Porthmadog with the North Wales Narrow Gauge Railways link terminus at Rhyd Ddu. Although some of the line was constructed between 1901 and 1906, it never opened and eventually became part of the Welsh Highland Railway.

The North Wales Narrow Gauge Railways (NWNGR) was a railway company that planned to build a number of inter-connected 1 ft 11+1⁄2 in narrow-gauge railways across North Wales. The first two of these lines - jointly known as the "Moel Tryfan Undertaking" - were authorised by Act of Parliament 1872 and were built and opened in the 1870s. The original main line ran from Dinas Junction to Bryngwyn and opened in 1877. The second line was a branch from Tryfan Junction to South Snowdon, though shortly after opening, the company designated the Tryfan Junction to Bryngwyn section as the branch, and the Dinas Junction to South Snowdon section as the main line.