Proper attic ventilation systems allow a continual flow of outside air through the attic, protecting the efficiency of the insulation and helping to lower temperatures in the living space. It consists of a blance between air intake (at your eaves or soffits) and air exhaust (at or near your roof ridge).
The FHA (Federal Housing Administration) recommends a minimum of at least 1 square foot of attic ventilation (both intake and exhaust) for every 300 square feet of attic space.