Thesis: The objective of this thesis is to contribute to economic literature by analysing three psychological determinants in the way individuals make decisions over time, using approaches and methodologies from economics and psychology. Thus, the first chapter of this thesis theoretically analyses the demand for commitment devices to overcome their own present-bias. This theoretical study is illustrated by a laboratory experiment on weight loss. The second chapter empirically examines the impact of working conditions on individuals’ health behaviours in the light of the psychological literature on self-control. The third chapter proposes a translation and validation of the Aspects of Identity Questionnaire and shows that the economic analysis of individual preferences can benefit from the reintroduction of the subjectivity of personal identity. Finally, the last chapter of this thesis explores the extent to which this subjectivity of personal identity can be important in understanding intertemporal choices.