The current research programme represents a rst step in the psychological analysis of on-line game playing. In the literature review presented in Chapter 1, Network Latency and 'game challenge' were identied as two important variables affecting participants' enjoyment of on-line games. The experiments presented in Chapter 2 define 'game challenge' in terms of levels of derived relational responding, and found that participants were able to consistently respond in accordance with both one and three-node derived relations in the context of a computer game. The presence of Network Latency in a game was found to be detrimental to the game playing experience, but increasing the length of those delays was not. The experiments presented in Chapter 3 defined 'game challenge' in terms of more complex forms of derived relational responding and found that participants were able to consistently respond in accordance with derived 'Same' and 'Opposite'relations in the context of a computer game. As in Chapter 2, the presence of Network Latency in a game was found to be detrimental to the game playing experience, but increasing the length of those delays was not. Participants were more successful at and preferred the simpler levels of the games examined in Chapter 3. Experiments in both Chapters 2 and 3 successfully modeled on-line game playing in terms of derived relational responding. The experiments reported in Chapter 4 were conducted in order to develop novel behavioural and physiological measures of enjoyment in game playing. It was found that participants' preference for games of varying diculty was dependent on their experience with those games. In addition, a novel methodology was developed for analyzing electro-dermal activity, which successfully differentiated games on the basis of the preference shown for them by participants. Finally, Chapter 5 reviewed the relevance of the research findings to the research literature.