This chapter deals with a brief introduction regarding Millimeter-waves (mm)-waves and discusses methods for channel propagation and characterization. The high frequency of mm-waves and their propagation characteristics motivate researchers to apply mm-waves for various applications, including transmission of large amounts of data, cellular communication, radar, and so on. With its huge amount of available bandwidth, mm-waves are used to transmit large amount of data. The channel models at mm-wave are different from other frequency bands because the propagation environment has a different effect on smaller wavelength signals. Mm-waves have a special propagation features because of very small wavelength compared to the size of most of the objects and devices in the environment. The applications of mm-waves are enormous in areas such as Wireless Local and Personal Area Networks in the unlicensed band, 5G cellular systems, vehicular area and ad hoc networks, as well as wearable devices.