INTRODUCTION: The history of the Railway Companies begins long before the development of the Greek State on the well-known current borders. During the period of the second half of the 19th century we have the timid steps for the development of railways in the newly established Greece, but in the region of Macedonia and Thrace, there was greater growth with the help of foreign capital. Sultan Abdul Aziz foreseeing the need of the countries of Central Europe (Germany and Austro-Hungary) for a way out to the Near and Middle East and realizing the development of the new means of transport of the railways, he ceded to foreign companies (German, Austrian, French, Belgian and Italian) the construction and operation for a specific period of time of networks, which would connect Constantinople (Istanbul) with Central Europe, The Thessaloniki with Monastiri and Skopje and then with Central Europe, but also the port of Alexandroupolis with Andrianople (Edirne) and Sofia, because of the strategic importance it had for trade. The order in which the description of the networks follows is slightly temporal, without distinguishing between the Greek state and the Othoman Empire. (For more information click on the red name of each company).

- Sidirodromos Athinon - Pireos SAP (Athens-Piraeus Railway): Since 8/8/1868 until 1/4/1926 with the establishment of EHS and their subordination to it.

- Compagnie Generale d' Exploitation des Chemins de Fer de la Turquie d' Europe (General Company for Operation of European Turkey Railways): Since 1873 until 1/1879 with the transfer of the project to the Compagnie d' Exploitation des Chemin de Fer Orientaux (CO).

- Compagnie d' Exploitation des Chemin de Fer Orientaux C.O. (Eastern Railways Exploitation Company): Since 1/1879 until 25/12/1936 with their nationalization and absorption by the Turkish Railways TCDD.

- Sidirodromos Thessalias STHS (Thessaly Railway): Since 25/10/1882 until 1955 with its absorption by the SEK.

- Sidirodromi Pireos - Athinon - Peloponnisou SPAP (Piraeus-Athens-Peloponnese Railways): Since 1/12/1882 until 1962 by joing the SEK.

- Sidirodromi Attikis SA (Attica Railways): Since 12/1882 until 1929 by the transferring the Neo Iraklio - Lavrio section to the SPAP.

- Sidirodromos Pirghou - Katakolou SPK (Pirghos-Katakolon Railway): Since 13/6/1883 until 1951 by the subscribing to SPAP.

- Eteria Mesimvrinon Sidirodromon Ellados EMSE (Company of Meridian Railways of Greece): Since 28/6/1889 until 1899 with its integration in SPAP.

- Societe du Chemin de Fer Ottoman Salonique - Monastir SM (Union of Othoman Railways Thessaloniki - Monastiri): Since 1890 until 17/10/1925 when the Greek part of line was acquired by the SEK.

- Sidirodromi Vorioditikis Ellados SVDE (North-Western Railways of Greece): Since 3/1890 until 1952 with the bankruptcy and their subordination to the SPAP.

- Enotikos Sidirodromos Thessalonikis - Constantinoupolis (Jonction Salonique-Constantinople J.S.C.): Since 1892 until 1921 when the line was acquired and included in the SEK and so it ceased to have a reason to exist.

- Eteria Ellinikon Sidirodromon EES (Hellenic Railways Company): Since 26/2/1902 until 18/3/1920 with the establishment of SEK.

- Sidirodromi Ellinikou Kratous SEK (Hellenic State Railways): Since 18/3/1920 until 1/1/1971 with their reorganization in OSE.

- Topiki Sidirodromi Macedonias TSM (Local Railways of Macedonia): Since 5/2/1924 until 1932 with the start of dismantling of the line.

- Elliniki Ilektriki Sidirodromi EHS (Hellenic Electric Railways): Since 1/4/1926 until 1/1/1976 with their acquisition by the Greek state and their renaming to HSAP.

- Ilektriki Eteria Metaforon HEM (Electric Transport Company): Από 1/4/1926 until 14/12/1970 with their acquisition and the establishment of HLPAP.

- Compagnie Franco-Hellenique de Chemin de Fer C.F.F.H. (French-Greek Railway Company GES): Since 1929 until 7/5/1954 with the acquisition of Alexandroupolis - Ormanio network by the SEK.

- Orghanismos Sidirodromon Ellados OSE (Hellenic Railways Organization): Since 1/1/1971 until 2007 with the transfer of the transport project to TRAINOSE.

- Ilektriki Sidirodromi Athinon - Pireos HSAP (Athens-Piraeus Electric Railways): Since 1/1/1976 until 17/6/2011 with establishment of STA.SY.

- Proastiakos Sidirodromos (Proastiakos Railway): Since 2003 until 7/2007 with its absorption by TRAIOSE

- TRAINOSE s.a.: Since 2007 until today.

- Statheres Sigkinonies A.E. STA.SY. (Fixed Transport S.A.): Since 17/6/2011 until today.