Delay discounting is the devaluing of future outcomes relative to present outcomes. The work in this dissertation aimed to contribute to answering the question: What are the psychological drivers of delay discounting behavior?Applicable literature was reviewed for clues to this question.Several hypotheses, previously largely empirically neglected, were examined: economic reasons, uncertainty about the future, pain of abstinence, differences in construal level, optimism, intrapersonal empathy gap, present utility, and future self as other.Additionally, a synthesis of relevant data from the literature led to the proposal of a novel hypothesis, dual-system competition.Eight empirical studies were performed to test some of the candidate causes of delay discounting.Studies 1 and 2 had mixed results that may imply that differences in construal level play a role in discounting behavior.Studies 3 and 4 tested the notion that self control is required to resist discounting, but failed to support this idea.Study 5 returned mixed results that may indicate that people fail to adequately anticipate their future wants and needs (intrapersonal empathy gap hypothesis).Study 6 indicated that anticipated changes in income do not motivate delay discounting behavior.Study 7 showed that field dependence is not related to discount rates.Finally, Study 8 suggested that discounting behavior may depend upon the activation of the fast/automatic cognitive system relative to the slow/effortful cognitive system.