This chapter focuses on experimental findings of millimeter wave effects on subcellular and cellular levels, effects on cellular proliferation and gene expression, effects on excitable tissues, involvement of nervous and immune systems in millimeter wave effects, physiologic effects of high power millimeter waves. The millimeter wave E-field distribution is measured with E-field probes. As the size of the commercially available E-field probes is relatively large, their use in the near field of an antenna is limited. As the wavelengths of millimeter waves are small in comparison with the size of human body, the geometrical optics concepts can be applied for calculations of interaction of millimeter waves with skin. Absorption of millimeter wave energy of any intensity will produce a temperature elevation. The eyes, located on the surface of the body like skin, are directly exposed to millimeter wave irradiation. Exposure to high-intensity millimeter waves can produce adverse effects in the eye.