This paper considers the relationship between the economic concept of time preference and relevant concepts from psychology and biology. Using novel data from a time diary study conducted in Ireland that combined detailed psychometric testing with medical testing and real-time bio-tracking, we examine the extent to which individual differences in financial discounting are related to underlying biological and psychological differences. The paper finds that financial discounting is related to a range of psychological variables including consideration of future consequences, self-control, conscientiousness, extraversion, and experiential avoidance, as well as being predicted by heart rate variability and blood pressure. (JEL: D01, D9, C81)