The present invention provides a lightweight protective helmet having an improved ventilation system therein. The protective helmet comprises an outer shell and an inner liner that are joined together to form a shell/liner composite. The ventilation system interacts with one or more ventilation ports in the protective helmet to control the flow of ambient air in and out of the interior of the protective helmet. The ventilation system may be integrated or encased within the shell/liner composite, or it may be adapted to be used on the exterior of the helmet. In addition, the ventilation system may include one of several types of interchangeable insert members to allow active or passive control of ambient air into the interior of the helmet.