Originally Posted by RfromRMC
OK, isn't adultery a civil offense, not a criminal one? I.e, someone could sue you for divorce, but if you're in an agreed open marriage, it's not considered adultery? (I admit I'm not legal expert here!)
In the United States, laws vary from state to state. In those states where adultery is still on the statute book (although rarely prosecuted), penalties vary from life sentence (Michigan), to a fine of $10 (Maryland), to a Class I felony (Wisconsin). In the U.S. Military, adultery is a potential court-martial offense. The enforceability of adultery laws in the United States is unclear following Supreme Court decisions since 1965 relating to privacy and sexual intimacy of consenting adults. However, occasional prosecutions do occur.
Admittedly this is just from Wiki and might be totally out to lunch but it is interesting never the less.