Espionage or spying involves an individual obtaining information that is considered secret or confidential without the permission of the holder of the information. Espionage is inherently clandestine, lest the legitimate holder of the information change plans or take other countermeasures once it is known that the information is in unauthorized hands.[clarification needed this should be clearer lest people not understand it]
Espionage is usually part of an institutional effort by a government or corporation, and the term is most readily associated with state spying on potential or actual enemies primarily for military purposes. Spying involving corporations is known as industrial espionage.
One of the most effective ways to gather data and information about an enemy (or potential enemy) is by infiltrating the enemy's ranks. This is the job of the spy. Spies can bring back all sorts of information concerning the size and strength of an enemy army. They can also find dissidents within the enemy's forces and influence them to defect. In times of crisis, spies can also be used to steal technology and to sabotage the enemy in various ways. Counterintelligence operatives can feed false information to enemy spies, protecting important domestic secrets and preventing attempts at subversion. Nearly every society has very strict laws concerning espionage, and the penalty for being caught is often severe. However, the benefits that can be gained through espionage are generally felt to outweigh the risks.
Further information on clandestine HUMINT (human intelligence) information collection techniques is available, including discussions of operational techniques, asset recruiting and the tradecraft used to collect this information.