Dishwasher plumbing

Do dishwashers have to be plummed into a garbage disposal?
Can they be plumbed directly into the sink trap if you have no garbage disposal?

Thanks in advance!
-Shawn

They make pipes with a connection to hook the DW drain hose into above the p-trap. It is highly recommended, and may be code in your location, to use an air gap in the countertop to prevent any backup in the drain from allowing that to back up into the DW. This is in lieu of a high loop from the DW in the discharge hose which helps, but does not prevent that from happening.

What you need is a dishwasher tailpiece. Here is an example...http://doitbest.com/Plumbing-66969-PVC+Dishwasher+Connection.dib