The Intelligence Agency is a Tier 2 government building in Civilization VI: Rise and Fall. It is built in the Government Plaza district and requires a Tier 2 government (Merchant Republic, Monarchy, or Theocracy) and a Tier 1 government building (Ancestral Hall, Audience Chamber, or Warlord's Throne).
While the Foreign Ministry and Grand Master's Chapel are often considered to be "niche picks" (meaning they are only suitable for a particular sets of civilizations in a specific situation), the Intelligence Agency has an impressive scope of usage. An extra Spy with increased Spy efficiency overall is nothing to scoff at, not to mention that is a bonus that literally every empire can employ well. This is pretty much the default Tier 2 government building and will do well in every situation no matter what.
Civilopedia entry Edit
There are many matters of state which need to be dealt with discreetly. There are matters whose practical solutions run at odds with the intended public image of the state and its leadership. Because of this, rulers have tended to rely on a small set of professionals who possess the discretion and stomach for the secret matters of state.
There are numerous and famous examples throughout history. Tales of spies are found in the Old Testament. Treatises on best practices for spying, deception, and misdirection were written in classical India and China. The Art of War by Sun Tzu possesses an entire chapter titled "Intelligence and Espionage," and the Arthashastra has one on spying, counterintelligence, and information warfare. King David IV of Georgia had mstovaris who kept him informed of various plots throughout his domain.
But the modern intelligence service can be traced to the work done by Francis Walsingham, the redoubtable spymaster and loyal servant of Queen Elizabeth I. To him and his staff we can trace methodical practices of coding and codebreaking, the overseeing of field agents, and reading other people's mail. We can neither confirm nor deny that he had an entire team who made clever gadgets for their spies, like laser pens and sports cars with ejector seats.