Security clearances are issued by many government agencies and can come in several different levels, offering different access to sensitive or classified material.

And even if you have the highest level of clearance, that's not an invitation to plunder all files.

You will likely see Onley materials you need to know about who get security clearances.

As a practical matter, they go to people who are intimately involved in the safety and defense of the United States and its allies.

Now, this is not all military business.

For example, there could be economic information or infrastructure details or negotiations with other countries, which might be considered highly sensitive and fall under this umbrella.

But all of this has to do with active government service.

So why should anyone who's left the government retain his or her security clearance?

Former employees of an agency have experience.

They have institutional knowledge, and the people who take over for them may need that.

Say you worked on some classified matter involving another country, and a new team comes in.

They need to know what you did.

This would assist the new team to be able to talk to you about the current situation as well.

In addition, some private industries defense contractors, for example, do work that requires private citizens to deal with sensitive government matters.

So having a security clearance outside the government can also be useful.

So why would anyone lose or have their security clearance revoked?

Usually that happens because they truly no longer need it or some conflict has arisen.

For example, they start working for a foreign, hostile government, or they just get into trouble.

They commit a crime or they're linked to some illicit or risky activity.