I want to focus on some of the limits of decision theory that are of interest to the philosophical concern with practical reasoning and rational choice. These limits should also be of interest to the social-scientists' concern with Rational Choice.Let me start with an analogy. Classical Newtonian physics holds good and valid for middle-sized objects, but not for the phenomena of the very little, micro, sub-atomic level or the very large, macro, outer-space level: different theories, concepts and laws apply there. Similarly, I suggest that we might think of the theory of decisionmaking as relating to middle-sized, ordinary decisions, and to them only. There remain the two extremes, the very ‘small’ decisions on the one hand and the very ‘big’ decisions on the other. These may pose a challenge to the ordinary decision theory and may consequently require a separate treatment.