The world-wide development of gaming machines has seen a large number of machine characteristics become an inherent part of gaming machine play. This book undertakes an examination of the relationship between the structural characteristics of gaming machines and player expenditure patterns. The book highlights original research that utilises player data from over 1000 Australian slot machines. The results suggest that both measures of expenditure examined, stake size and net profit, are related to machine characteristics. This finding provides a foundation for the discussion of individual player behaviour encompassing both learning and cognitive explanations of behaviour. A second study examines the expenditure patterns of over 500 individual players on Australian slot machines. The results indicated that certain slot machine characteristics are related to the amount staked, but not directly to the player's net loss. These results are discussed in the context of popular psychological explanations of human behaviour.