Head mounted displays (HMD) provide one means of displaying virtual environments. This paper assesses the state of HMD technology, with respect to the Virtual Reality (VR) goal of creating an environment which matches user's experience with the real world. We find that current HMDs fall short in important characteristics, such as resolution, field of view, and physical attributes. A system designer, familiar with these limitations, should be able to provide a suitable immersive virtual environment with the inclusion of appropriate graphics rendering techniques and virtual environment input/output devices.