About the author: Richard Shelby, a Republican senator from Alabama, serves as chairman of the U.S. Senate Select Committee on Intelligence.

Spying has been described as the world’s “second oldest profession”—and one that is, in the words of one former CIA official, “just as honorable as the first.”

Espionage has been with us since Moses sent agents to spy out the land of Canaan and the Philistines sent Delilah to assess Samson’s vulnerabilities. And spies are with us today. I will not attempt to cover the history of espionage from Biblical days to now, but I would like to take the opportunity to address some important recent history, and lessons from recent history, as...