The Southern Pacific (reporting mark SP) (or Espee from the railroad initials- SP) was an American Class I railroad network that existed from 1865 to 1996 and operated largely in the Western United States. The system was operated by various companies under the names Southern Pacific Railroad, Southern Pacific Company and Southern Pacific Transportation Company.

The original Southern Pacific began in 1865 as a land holding company. The last incarnation of the Southern Pacific, the Southern Pacific Transportation Company, was founded in 1969 and assumed control of the Southern Pacific system. The Southern Pacific Transportation Company was acquired in 1996 by the Union Pacific Corporation and merged with their Union Pacific Railroad.

The Southern Pacific legacy founded hospitals in San Francisco, Tucson, and Houston. In the 1970s, it also founded a telecommunications network with a state-of-the-art microwave and fiber optic backbone. This telecommunications network became part of Sprint, a company whose name came from the acronym for Southern Pacific Railroad Internal Networking Telephony.