This dissertation examines the use of metamaterial structures in millimeter-wave communication systems. Metamaterials, which are composite structures that have electromagnetic properties not found in nature, have been an area of explosive growth in academic research, including applications such as electrically small antennas, sub-wavelength imaging, and negative phase velocity transmission lines. In this dissertation, several potential applications of metamaterials are investigated, including new ideas related to negative forces. The design of highly directive antennas and their use in high data rate communication systems are emphasized. At millimeter-wave frequencies, specifically in a frequency band around 60 GHz, there is an enormous amount of available unlicensed worldwide spectrum available for data transmission. These systems may benefit from the knowledge of metamaterials and their integration with antenna systems. Although there are many challenges with working at such high frequencies and the metamaterials themselves are inherently dispersive and lossy, it will be demonstrated that useful structures can be designed and fabricated at these frequencies. Metamaterial-based artificial magnetic conductors were designed and it has been shown that they can handle 'gigabit per second' data rates. Moreover, superstrate structures were also designed to achieve near zero-index of refraction properties and, as a result, highly directive 60 GHz antenna systems. These metamaterial superstrate-based patch antennas were built and tested successfully with actual 'gigabit per second' data rates. Design and practical fabrication challenges associated with these millimeter-wave applications were addressed and will be reviewed.