Abstract: A modular mask system comprises a frame for fitting over a user's head, and a set of interchangeable mask components. Each interchangeable mask components can be removeably attachable to the frame. Each of the interchangeable mask components is one of a top panel, a side panel assembly, an eyepiece and a nosepiece. The interchangeable side panel assemblies can be different sizes to accommodate the user's face or have different patterns or have different configurations of ventilation holes. The interchangeable eyepieces allow the user to choose from dual lenses and a single shield. The eyepieces can include optically powered lenses, shaded lenses, dual lenses tinted lenses, photochromatic lenses and polarized lenses.