This thesis concerns epistemic and practical rationality. That is, it is about what to believe and what to do. In Chapter 1, 1 argue that theories of practical rationality should be understood as evaluating decisions as opposed to ordinary sorts of non-mental actions. In Chapter 2, I use the machinery developed in Chapter 1 to rebut 'Money Pump ' or 'Diachronic Dutch Book' arguments, which draw conclusions about rational beliefs and preferences from premises about how rational agents will behave over time. In Chapter 3, I develop a new objection to the Synchronic Dutch Book Argument, which concludes that rational agents must have probabilistic degrees of belief in order to avoid predictable exploitation in betting scenar...