Espionage is all about stealing secrets. Bad guys want to read your stuff. Good guys want to read the bad guy’s stuff.
This is the basic fundemantal function of espionage (colloquially, spying). This mix of art and science has its roots deep in human nature. We all want to know secrets, right? These roots run so deep many observers have called it the second oldest profession.
Espionage can be committed by an individual or a spy ring (a cooperating group of spies), in the service of a government or a company, or operating independently. The practice is inherently a secret one, since it is by definition something that is not welcome. While some spying is legal, in many cases it is not. It can be punishable by law, and if it is done against criminal groups or violent extremists can result in horrorible results for the spy who is caught.. Espionage can be considered as a subset of the broader construct of intelligence, which includes espionage as well as information gathering from public sources.
Espionage is often part of an institutional effort by a government or criminal group or maybe even a business. However, the term is generally associated with state spying on enemies. Spying involving corporations is known as industrial espionage. Others might simply call it competitive intelligence.
One of the most effective ways to gather data and information about the enemy (or potential enemy) is by infiltrating the enemy’s ranks. This is the job of the spy (espionage agent). Spies can bring back all sorts of information concerning the size and strength of enemy forces. 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 is related to intelligence. It concerns how to stop adversaries from collecting your information. Mature and effective counterintelligence activities might feed false information to enemy spies, protecting important domestic secrets, and prevent attempts at subversion.
Nearly every country 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 great enough that most governments and many large corporations make use of it.