Optimising and Satisficing under Partial Ignorance Frans Voorbraak In this paper, we study decision making in situations where the outcomes of the options are (in general) uncertain, without making the assumption that this uncertainty can be exactly quantified by means of a (single) probability measure. In such situations of partial ignorance, the traditional notion of optimising by maximising expected utility is in general rather weak, and we will discuss some proposals to augment or refine the criterion of maximal expected utility under partial ignorance. We will argue that one interesting possible refinement, which is related to the minimax regret rule originally proposed for decision under uncertainty, is best viewed as a rule for satisficing rather than optimising. To make this argument more precise, we first propose a formalisation of the notion of satisficing under risk. Keywords: decision making, partial ignorance, satisficing, minimax regret rule, independence of irrelevant alternatives.