An espionage balloon is a balloon used for spying.
During the Cold War, espionage balloons launched by the "Free world" had a secondary psychological warfare capability, carrying propaganda pamphlets and consumer goods (which were supposedly not freely available inside Communist states) that would be released or otherwise delivered onto enemy territories.
The advent of spy satellites, coupled with the end of the Cold War, have rendered espionage balloons obsolete.
Surveillance balloon programs include:
References
Espionage balloon Wikipedia(Text) CC BY-SA