EYP employs the following categories of personnel: The total number of people working for the agency is unknown and remains classified; the Greek media usually give figures of around 3,000.

The first modern Greek intelligence agency was created in February 1908, with the Information Department of the Ministry of Foreign Affairs fulfilling the role.

Events such as the Goudi coup and the Young Turk Revolution, prompted a sharp reduction of Greek activity in Macedonia and the eventual dissolution of the agency in November 1909.

Greek officers gained valuable experience on aerial reconnaissance and interrogation techniques from their French and British allies during their tenure on the Macedonian front.

Kondylis dissolved YGAK due to its close affiliation with Pangalos, leaving Greece without an intelligence agency for the next ten years.

On 5 November of that year, the service was dissolved by the Metaxas Regime & was replaced by the Deputy Ministry for Public Security (Υφυπουργείο Δημόσιας Ασφάλειας).

British reliance on the Albanian nationalist Balli Kombëtar militia created reluctance in the Greek intelligence community to collaborate with their erstwhile enemies.

An MI6 communication center was set up in the Bibelli Villa in north east Corfu and an Albanian language propaganda radio station operated from the Alkyonides Islands.

[9] Between 1952 and 1961 KYPE and its successor KYP conducted a campaign of cultural propaganda against the Greek communist party (KKE) and the United Democratic Left (EDA).

Reports were issued on the Trotskyist Fourth International as well as Titoism, those two currents of communism were to be reinforced in order to spread discord among the country's leftists.

KYP was controlled by the CIA; in the first eleven years of its history (1953–1964) its agents received their salaries from the Americans, not the Greek state, until Prime Minister Georgios Papandreou, enraged with this level of dependence, stopped this practice.

[12] After Andreas Papandreou came to power in 1981, he was determined to totally control the state apparatus, including the intelligence services, which historically had been staffed exclusively by people with right-wing political views.

In late May 1985, KYP agents monitoring the activities of the Soviet embassy in Athens realized that its sports secretary Sergei Bokhan had vanished under mysterious circumstances.

The latter two were acquitted after the judge presiding over their case claimed that they had the right to engage in industrial espionage as the technology in question belonged to a foreign nation.

The fact that the folders containing the documents were mailed through the regular post service and were not properly marked as classified also played a role in the court's decision.

New Democracy and CIA leveled the accusation that the PASOK political party was behind the creation of 17 November and Revolutionary People's Struggle (ELA) another Greek far left terrorist organization.

17 November had in fact been founded by Alexandros Giotopoulos, a staunch opponent of the Greek military junta of 1967–1974 and former member of the Paris anti–junta circles.

EYP had warned the central police headquarters that the leader of the local Palestinian student's union was an Islamic Jihad member and possessed weaponry on 3 April.

The level of EYP's awareness of Islamic Jihad's movements within the country led to allegations by a number of people including the former interior minister Ioannis Skoularikis that the bombing had been a false flag operation by either CIA or Mossad.

[21] The Officer also claims that all the evidence he had on this issue was also turned in to the Greek parliament during their investigation of the events of Cyprus (Later to be known as the Cyprus File), adding more details and claiming that although he was sending important intelligence signals to his superiors in Greece, he was getting no reply or instructions, including after informing them of the Turkish Military movements in the area saying " “It was as if they already knew everything and didn't need any additional information.” [22] In 2022, it was revealed that the National Intelligence Service tapped the mobile phone of opposition politician Nikos Androulakis, which led to immediate resignation of Greece's intelligence chief and the head of his personal office.

[24] The agency's motto is the ancient Greek phrase "Λόγων ἀπορρήτων ἐκφορὰν μὴ ποιοῦ" (translated roughly as "Do not discuss confidential affairs"), a quote attributed to the Corinthian tyrant and philosopher Periander.