Is there an understanding between nations that they will spy on each other?

I doubt that every nation engage in espionage. But the ones with the most at stake are surely in the forefront of the intel biz…making sure that nothing gets compromised and if things do get compromised that they are able to react to any threat.

“Does every nation engage in espionage?”
Yes.

Yes, every nation engages in espionage (to different levels).

No, there are no spy trades.

You might find this interesting.

Spy satellites are abundant flying around the globe. only the countries that can afford the satelittes are usually spy-bound on each others country. armed satelittes are my main concern.

Oh yeah.Spy hard.

There are many types of intelligence gathering. However, human intel is still the preferred method of superpowers, while it is backed up with electronic intel

I’m sure there is still a lot of cloak and dagger stuff going on between nations that need to worry about that kind of thing. I’d bet most spying is done electronically these days… why risk a highly trained human when a well programmed computer/robot/satellite will do?

Every nation has some kind of intelligence gathering organization and it is widely accepted practice. Spy trades arent as common as you think as it is easier to keep track of the enemy you know then the one you do not, so it is usually not in your best interest to rid yourself of a foriegn countries known spy. Back during the cold war the US and Soviet Union played the occasional game of revoking visas for spies. Spies were seldomly arrested, though occaisionally deported

The highly trained human can offer insights into what he has seen firsthand that electronic intel is incapable of offering.

Since when has risking highly trained humans meant diddly squat to those who send them into harm’s way?