If it is a subpoena to appear in court for any reason you may be held in contempt for failure to appear. If it is a summons for you to appear as a defendant in some kind of civil action you may be...
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...