A spy ship or reconnaissance vessel is a dedicated ship intended to gather intelligence, usually by means of sophisticated electronic eavesdropping. In a wider sense, any ship intended to gather information could be considered a spy ship.

Technical research ships were used by the United States Navy during the 1960s to gather intelligence by monitoring, recording and analyzing wireless electronic communications of nations in various parts of the world. At the time these ships were active, the mission of the ships was covert and discussion of the true mission was prohibited. The mission of the ships was publicly given as conducting research into atmospheric and communications phenomena. Their designation was AGTR – Auxiliary, General, Technical Research – but it was more or less an open secret that this was a euphemism and they were commonly referred to as "spy ships".