A word from the National Security Agency:

Responsible Citizen: Americans expect NSA to conduct its missions within the law. But given the inherently secret nature of those missions, how can Americans be sure that the Agency does not invade their privacy? The 4th Amendment of the Constitution demands it... oversight committees within all three branches of the U.S. government ensure it... and NSA employees, as U.S. citizens, have a vested interest in upholding it. Respecting the law is only a part of gaining Americans' trust. The American people need to know, within the bounds of operational security, what NSA does and why they do it, and how they work within the Intelligence community and the Department of Defense to protect the Nation's freedom...