The first railway signalling in Greece was installed on the Athens–Piraeus Railway at the turn of the 20th century, when semaphores and boards were added with the line's electrification. Other Greek trains at that time were controlled by signals given manually by station masters. During World War II, German occupation forces installed mechanically operated semaphore signals at the entrance to all stations, with some light signals at busy stations. Modern signalling is provided through colour light signals. Radio communication between train stations and drivers was introduced in 1973 and digital communication is an ongoing present-day introduction.

On lines currently operated by the Hellenic Railways Organisation (OSE), signalling was not installed until World War II. There were few trains running and all traffic control was performed by the station masters (Greek: Σταθμάρχης). They controlled trains by hand signals and whistles and also delivered written orders to the train drivers for special operating procedures. Station managers were coordinated by morse-code landline telegraph and, later, by telephone.

The first semaphore signals were installed by the German military occupation forces during World War II and are almost identical to the "H/V" signalling system of the Deutsche Reichsbahn of the same period. Main signals consisted of two-arm semaphores and distant signals of yellow disks. These signals controlled the entrance to stations and were operated mechanically by wire from the station platform. Usually on each direction there was one semaphore controlling the entrance to the station, preceded by a distant signal. Some of them still survive, but they are no longer operational.

Local signalling using two-aspect colour light signals controlled by the station manager was installed at some busy stations like Athens/Larissis Station, Athens/Peloponnese station, Inoi junction etc.

All current aspects of railways signalling are described in the document "Γενικός Κανονισμός Κυκλοφορίας - Μέρος Α - Κανονισμός Σημάτων και Παραρτήματα I, II, III, IV, V & VI". This is a collection of different regulations, the main part covering semaphore signals and lineside signs, with appendices covering new signalling systems. It was issued in electronic format by Hellenic Railways Organisation in 2009. The contents of this document include:

Semaphore signals followed the German pattern and consisted only of home signals (German: Einfahrsignal) with the corresponding distant signals, covering the entrance to stations and are described in Chapter II of the Signalling Regulation. There were no starting semaphore signals (German: Ausfahrsignale), as the trains were signalled out by the Station Master in person, holding up a staff with a green disk and blowing his whistle. This practice was followed when colour light signals were first installed in the sections Athens–Inoi Junction and Thessaloniki–Platy, even though the new system included starting signals, but it was abandoned later, with the introduction of the current signalling system.

Around 1973, as a result of a serious train accident that took place between Doxaras and Orfana stations in Thessaly, the OSE installed VHF/FM radios in all stations and driving cabs. In many cases the orders are transmitted over the radio by station masters, instead of being handed out in printed form. In the past OSE used ten different VHF frequencies. An allocation of 150.05 to 151.6 is reserved for the VHF/FM service. Today operations use four channels as follows:

The suburban section from Acharnai Railway Center to the Athens International Airport station uses commercial TETRA radio instead of VHF/FM.