The tremendous growth of mobile wireless devices in various form factors requires efficient, compact, and multi-function antennas, capable of providing high data rates at multiple application bands. Modern wireless devices incorporate a number of different antennas to provide services for cellular voice, video, data, Wi-Fi, and GPS connectivity, across multiple bands. High data rate requirements also demand the design of multiple input multiple output antennas in order to implement spatial multiplexing and diversity schemes. Reconfigurable antennas possess the ability to change their characteristics (frequency, pattern, polarization) as per application demand. Dynamic alteration of the radiation characteristics makes them a suitable candidate for multi-function, small size wireless devices, where the requirement of multiple antennas can be circumvented by a single reconfigurable antenna. Dielectric resonator antennas (DRAs) offer a number of benefits over the conventional conductor-based antennas. The advantages include high radiation efficiency, small size, and a versatility of feed mechanisms. Despite many benefits, however, the size of the DRA must be excessively miniaturized to make their integration feasible in wireless devices of small size and various form factors. The aim of this work is to devise some novel reconfiguration and simultaneous miniaturization techniques for DRA based antennas. Hybrid structures comprising of DR and other resonant structures (like microstrip patch, slots) have been explored previously for enhancement of impedance bandwidth, multi-band, and wideband applications. Hybrid antenna structures combine the desirable features of both resonators and are much beneficial to meet the diverse application demands. This work proposes a hybrid combination of DR element, with ground plane (GP) slots to design compact, efficient, and multi-function reconfigurable antennas. The reconfiguration properties of the proposed antenna structures satisfy multiple application band requirements, while the miniaturization aspects assist to save valuable space in small devices. The GP slots can either be employed as a resonant structure or act as a defected ground structure (DGS) for the resonant DR element. The proposed technique has been applied for the design of frequency reconfigurable (FR), single-input-single-output (SISO), multiple-input-multiple-output (MIMO), and frequency plus pattern reconfigurable antenna designs. A few novel designs are presented in the current dissertation that effectively combine the GP slots and the DR resonances to obtain efficient, multi-band, antenna structures for SISO as well as MIMO applications. The combination of probe-fed and microstrip line fed DR elements with GP slots has thoroughly been analyzed and designed with an emphasis to get higher tuning ranges and better isolation. In almost all designs, the reconfiguration aspect has been incorporated by placing switches on the GP slots, which in turn alter the slot length and result in achieving either frequency or pattern reconfiguration.