All choices are economic decisions, and this is true because mobile organisms run on batteries. For them the clock is always ticking and their battery draining so every moment represents a choice of how to invest a bit of energy. From this perspective, all choices – those made and those not made – engender costs and yield variable future returns. There is no more fundamental stricture for an organism than to behave so as to recharge their batteries; consequently, each moment of existence is attended by the need to value that moment and its near-term future quickly and accurately. The central issue of neuroeconomics is valuation – the way the brain values literally everything from internal mental states to experienced time (the neuroscience part), and why it should do so one way and not another (the economics part). All these valuations have now begun to be probed in experiments by pairing quantitative behavioral and computational modeling with neuroimaging or neurophysiological experiments. This new field seeks to connect the underlying biology of the brain to one of the most important functions carried out by all humans – choice. A deeper understanding of this connection, its detailed physical basis, and its evolutionary origins will equip us with the ability to understand more fully how brain damage, mental illness, and even extreme psychological experiences impact us as decision-makers.