This thesis describes two studies aiming to enhance the speed, accuracy and practicality of the P300 Speller. The first study introduces the Inverting paradigm, which is based on the hypothesis that a modification in the visual stimulus paradigm in order to increase the stimulus saliency and strength might enhance the physiological response and hence system performance. The second study compares Speller performance using a minimal four electrode set, versus the 32 and six electrode sets previously used and described in literature. The Inverting paradigm significantly improved Speller speed and accuracy, along with an increase in the physiological response. The minimal electrode set maintained comparable levels of performance and hence increased the system practicality.