Digital games provide the most engaging interactive experiences. Researching gameplay experience is done mainly in the science and technology (e.g., human-computer interaction, physiological and entertainment computing) and social science (e.g., media psychology, psychophysiology, and communication sciences) research communities. This thesis is located at the intersection of these research areas, bringing together emerging methodological and scientific approaches from these multi-faceted communities for an affective ludology; a novel take on game analysis and design with focus on the player. The thesis contributes to game research with three important results: (1) the establishment of an objective/subjective correlation methodology founded on psychophysiological methods, (2) the creation of a formal theoretical framework in which to conduct user experience (UX) research related to games, and (3) the combination of results regarding cognitive and emotional factors for describing, defining, and classifying the interactive relationship between players and games. Two approaches for measuring gameplay experience are used in this thesis. First, objective assessment of physiological user responses together with automated event-logging techniques, so called game metrics, allows collecting essential player- and game-related variables for a comprehensive understanding of their interaction. Second, using psychometric questionnaires allows a reliable assessment of players' subjective emotion and cognition during gameplay. The benefit of psychophysiological methods is that they are non-intrusive, covert, reliable, and objective. To fully understand psychophysiological results, a correlation between subjective gameplay experience ratings and psychophysiological responses is necessary and has been done in this thesis and prior work it builds on. This thesis explores objective and subjective assessment of gameplay experience in several experiments. The experiments focus on (1) level design implications from psychophysiological and questionnaire measurements, (2) the impact of form and age on subjective gameplay experience, (3) the impact of game audio and sound on objective and subjective player responses, and (4) the impact of game interaction design on and the relationship between experience and electroencephalographic measures. In addition, the thesis includes a theoretical framework for UX research in games, which classifies gameplay experience along the dimensions of abstraction and time. One remaining conceptual and empirical challenge for this framework is the huge variety of vaguely defined experiential phenomena, such as immersion, flow, presence, and engagement. However, the results from the experimental studies show that by establishing correlations between psychophysiological responses and questionnaire data, we are approaching a better, scientifically grounded, understanding of gameplay experience. Many possibilities open from here. More detailed analyses of cognition will help us understand to what extend gameplay experience depends on emotional or cognitive processing. In addition, the inclusion of more complex and detailed gameplay metrics data together with psychophysiological metrics will enable a comprehensive analysis of player behavior, attention, and motivation. Finally, the integration of new measurement technologies in interactive entertainment applications will not only allow a detailed assessment of gameplay, but also improve physical and mental interaction with future games.