A summons from WHO, for WHAT? Call whoever or whatever agency the summons is supposed to have come from and check on it. Do you REALLY want to take a chance on not appearing?
What kind of "summons" are you asking about? A traffic summons (ticket), or a summons (subpoena) from court? Not responding to the traffic court summons can get your drivers license suspended. Not...
There will be an instruction sheet that accompanies the summons. You are required, by law, to follow those instructions to the letter. If you don't, a search warrant will be issued for your arrest...