It is essential to seek out enemy agents who have come to conduct espionage against you and to bribe them to serve you. Give them instructions and care for them. Thus doubled agents are recruited and used.
— Sun Tzu

We have some material on spying by a major government on the tech industry. Industrial espionage.
Julian Assange espionage quote

This is the wonderful thing about espionage, nothing exists any more.
— William Stephenson

I'm sort of fascinated by the whole espionage crime thing.
— Aaron Eckhart

When I accepted the commission, I had something of an epiphany in the research I did about the agency, actually the science of espionage. I realized there is a connection between the sciences and the invisible forces of man.
— espionage quotation by James Sanborn