[Mark17]

Isn’t it illegal to tape someone, without their knowledge?

[Leep]

“Isn’t it illegal to tape someone, without their knowledge?”

only if you are not a democrat.

[The people have spoken]

“Isn’t it illegal to tape someone, without their knowledge?”

No, not in Washington. Only one party needs to be aware of the taping for it to be legal.

[Buckeye McFrog]

Isn’t it illegal to tape someone, without their knowledge?

Depends on the jurisdiction. Some states allow one party to tape the other without consent. I am pretty sure that it's illegal inside a secured Federal facility however.

[Krosan]

As far as I understand it is illegal only in California, Connecticut, Florida, Illinois, Maryland, Massachusetts, Montana, New Hampshire, Pennsylvania and Washington.

http://www.dmlp.org/legal-guide/recording-phone-calls-and-conversations