Espionage Technology allows players build and launch Espionage Probes to spy on an enemy planet, revealing the planet’s Buildings, Fleets, Defenses, and Research/Technology Levels. The amount of information revealed depends on the difference between the two players' Espionage Technology levels. The higher your Espionage Technology level is compared to your target, the more information your spy report will contain. Conversely, if you are the target of a spy mission, having a higher Espionage Technology level than your opponent will limit the information obtained his spy probes obtain. A more complete spy report can also be obtained by sending a larger number of espionage probes on the spy mission, which increases the likelihood of their being shot down (but does not stop them from transmitting their report before they die).
Your level of Espionage Technology also determines the amount of information you get about an incoming foreign fleet on your Overview screen’s Flying Fleet Overview display. Incoming fleets from another player are indicated by a red number.