What sense can we make of Hume’s notorious distinction between impressions and ideas? This chapter looks at two sense-datum theories of experience that offer competing accounts of the contrast between sensation and imagination. John Foster’s two-level account of experience presented in The Case for Idealism and The Nature of Perception is contrasted with Bertrand Russell’s discussion of sensation, imagination and memory in The Theory of Knowledge manuscript. The key elements of both approaches are sketched. Foster’s appeal simply to a ‘subjectively manifest’ difference is rejected as inadequate. A problem with Russell’s conception of experience of past is canvassed, and then further elaborated in relation to previous awareness condition on personal memories. The contrasting views of memory is then extended to the case of imagination. The chapter concludes with more general morals to be drawn about the relation between the first person perspective on experience and the underlying psychological properties which explain experience’s being so.