||User requirements for access to a diversified range of advanced wireless telecommunication services have resulted in a rapid technological push to develop novel antenna design solutions for future generation wireless communication systems These include Multi-Mode Multi-Band antennas, Multi-Function and MIMO. One promising technology to meet the future requirements is the reconfigurable antenna. A reconfigurable antenna can virtually or electronically change the shape and size of its antenna geometry by utilizing electronic circuits inside the antenna such that the antenna can be reconfigured to work in different operating bands or standards for various functions when necessary. In this thesis, four new and novel contributions to reconfigurable antennas are described. The first contribution is the reconfigurable antenna for a portable wireless communications device. Two novel reconfigurable antennas have been designed. The first design supports Quad-band GSM and UMTS (3G) and the second design supports Quad-band GSM, UMTS (3G), Bluetooth and WLAN. Different active switches are also implemented on the reconfigurable antennas and the performance is compared and investigated. The second contribution involves a novel method to enhance the isolation between two closely packed antennas operating at the same frequency. A design of a USB dongle MIMO antenna for 2.4GHz WLAN Band is presented. The third contribution is a practical design of a low cost reconfigurable Landsdorfer planar antenna array. The antenna array can have a 360-degree coverage in azimuth and allows a wide variety of directive beams to be electronically selected while maintaining a simple structure, ease of manufacture and low cost with high efficiency. Finally, in the fourth contribution, a compact and low-cost direction finding antenna system is proposed. The uniqueness of this compact antenna design is that it can reconfigure either a cardioid pattern or a directional beam pattern in order to detect the incoming RF signal from the source.