Is it illegal for someone to spy on you in your home without your permmission?
My friend lives in an apartment complex, and has recently discovered that her upstairs neighbor has seem to put a small camera down through the dry wall, and is spying on her throughout her apartment. Does anyone have a written solution?

A written solution? This is criminal activity. She should call the Police. Some States have HEAVY fines and prison sentences for this same thing.

I'm an investigator. My senses are tingling. I hope I'm wrong.

Are you the landlord, asking in advance? Otherwise... not so sure about this question from the standpoint of a tenant who has not yet contacted the Police.

Yes, you call the police

This is a fairly new area of law. ANY question on law needs to include your general locale as laws vary by area.

But your friend should be going to the police about this immediately.