Ice Wine is produced from grapes that are picked within a few hours of the first hard frost. The frost freezes the ripe grapes, concentrating the sugars and flavor. The grapes must be picked and processes while frozen or the grapes will rot.
A warning, some wineries cheat and freeze the grapes after picking them. Laws passed in 2003 prevent these wineries from calling the product Ice Wine. The Ice Wine or Eiswein are the real things.
Ice wines are produced in Germany, Austria, Canada and the US.