OBS - Croatia's intelligence agency, the Obavestajna Bezbednostna Služba.

OFFENSIVE PENETRATION OPERATION - Infiltration of an agent into a target group or organization.

610 OFFICE (The) -  A Chinese extra judicial intelligence agency, under the command of the Politburo, with the purpose of carrying out surveillance, intel gathering and ultimately destroying the Falun Gong. Carried out spying on Falun Gong organisations the world over, notably in the United States, Canada and Australia. Since 2003, it's role has been expanded to more varied forms of social control and intelligence.

OFFSITE - A covert site or facility situated away from a field office.

OGPU - The Joint State Political Directorate (also translated as the All-Union State Political Administration and Unified State Political Directorate) was the secret police of the Soviet Union from 1923 to 1934.

OKHRANA - Secret police under Russian tsars 1881-1917.

ONE-TIME PAD - Strings of random numbers for singular, one-time use as a key in enciphering and deciphering messages. the proper use of a one-time pad renders a message mathematically unbreakable.

OP - Observation Post.

OPEN-SOURCE - intelligence gained from public materials.

OPERATION GOLD (also known as OPERATION STOPWATCH by the British) - A joint 1950′s American-British operation which was funded by the United States and involved creating a secret tunnel half a kilometer long which entered the Soviet-occupied zone in East Germany.

OSA - Official Secrets Act. Legislation that protects official information and state secrets relative to national security.

OSINT - Open Source INTelligence. Intelligence information derived from publicly available sources such as government reports, financial reports, books, movies or realistic TV shows such as "The Americans".

OSS - Office of Strategic Services; the U.S.'s WWII intelligence, sabotage, and subversion organization. Was at first dubbed by some "Oh So Secret," "Oh Such Snobs," “Oh So Social”.

OSTER, Hans - Spy.

OUTRIDER - A wheel artist responsible for ensuring that the target does not get outside the floating box of surveillance vehicles. (See also FLOATING BOX.

OVERT TARGET - Deliberately attempts to draw attention and drain the resources of an intelligence agency or security service. Occasionally a decoy.