The vent is on the top rear as with most over the range microwaves. You can vent it traditionally (ie to an outside vent) or recirculate it, which means just that--the air recirculates as opposed to being vented outside. There is an air filter used for this that comes with the unit. I have done it both ways, depending on the house. In my opinion it's always better to vent outside but sometimes there may not be an existing outside vent to attach to so unless you want to make one by cutting a hole through an outside wall, you would simply use the recirculating option. Hope that helps!