Multi-Carrier Code Division Multiple Access (MC-CDMA) exploits the joint benefits of Direct-Sequence (DS) CDMA and Orthogonal Frequency Division Multiplexing (OFDM). Hence, MC-CDMA exhibits high spectral efficiency and substantial benefits from the frequency diversity provided by frequency selective fading channels. This dissertation investigates several aspects of MC-CDMA. Firstly, the Peak-to-Average Power Ratio (PAPR) of the MC-CDMA signal is analysed. It was shown that the PAPR is characterised by the aperiodic correlation properties of the spreading sequences employed. Several orthogonal spreading codes were investigated in terms of their PAPR and it was found that the PAPR can be upper bounded by 3dB when employing orthogonal complementary codes in the context of low number of sub-carriers. Secondly, the application of adaptive modulation to MC-CDMA was studied. The optimum mode switching levels for generic adaptive modulation schemes were derived first and then, the performance of adaptive-modulation assisted MC-CDMA was analysed for transmission over various propagation scenarios. When space-time block codes were combined with adaptive-modulation assisted MC-CDMA, as expected the SNR gains of adaptive modulation over fixed-mode modems were found to decrease. Lastly, three types of reduced-complexity despreading schemes were proposed with an application to MC-CDMA in mind and the BER performance as well as the achievable complexity reduction were investigated.