olemus
luure (2) alaliik, tegevus mitteavaliku teabe kogumiseks
inimagentide ja/või tehniliste vahendite abil,
sisaldab tavaliselt ka sidemete ja võimaluste loomist
otsustajate ja arvamusekujundajate mõjutamiseks;
täpsem määratlus sõltub kontekstist ja õigusruumist

Wiktionary:
the act or process of learning secret information through clandestine means

ülevaateid
http://criminal.findlaw.com/criminal-charges/espionage.html

http://legal-dictionary.thefreedictionary.com/espionage

https://en.wikipedia.org/wiki/Espionage

https://warwick.ac.uk/fac/soc/pais/people/aldrich/vigilant/espionage_and_intelligence_viewpoints.pdf

https://networks.h-net.org/node/28443/pages/42792/syllabus-intelligence-and-espionage-20th-century-jordan

https://www.asil.org/insights/volume/17/issue/10/economic-cyber-espionage-and-international-law-controversies-involving

http://www.digitalbookindex.org/_search/search010hstespionagea.asp

ajalugu
https://www.deutsches-spionagemuseum.de/en/espionage

http://www.english-online.at/government/espionage/history-and-methods-of-spying.htm

https://espionagehistoryarchive.com/

https://en.wikipedia.org/wiki/History_of_espionage

https://en.wikipedia.org/wiki/Cold_War_espionage

https://irp-cdn.multiscreensite.com/cadac795/files/uploaded/482512.pdf

https://icds.ee/wp-content/uploads/2019/11/ICDS_Analysis_Russias_Espionage_in_Estonia_Juurvee_Perling_November_2019.pdf

vt ka
- küberspionaaž
- majandusspionaaž
- tööstusspionaaž