Legal v/s Ethical

hi
  It is always a debatable issue, as to what is basic difference in legal actions verses Ethical action.
 How do one know his action is  legal and / or ethical.
 It is possible that an action is legal but not ethical?
or
is it possible that an action is ethical but not legal?

What to do when you are at a cross road of selecting any one?

any answers/

Amit