The first full investigation into the methods of radio espionage during the First World War. The rapid development of scientific and technological progress and the militarization of society have significantly increased the role of communications during combat operations. The success of military operations often depended on the rapid transmission of orders and information, and the failure of his plans depended on the ability to recognize the enemy’s intentions. The defeat of Samsonov's 2nd Russian Army in East Prussia was the first resounding success of the German army, and it was carried out on the basis of an intercepted Russian radio telegram. Subsequently, eavesdropping on telephone and telegraph conversations, radio interference, and radio disinformation were actively used on all fronts. The book tells about the methods of radio intelligence and espionage in the First World War. How certain methods of radio reconnaissance changed depending on the front, how naval radiotelegraphy worked and how naval codes were broken, how phones were wiretapped on the Russian (Eastern) and French (Western) fronts, who was responsible for wiretapping and how the received materials were processed, what radio interference was created for enemies and, finally, how misinformation was supplied to the enemy. For the first time, the methods of secret war on the air of the First World War are examined in detail in a separate publication, which is supplemented with previously unknown photographs.