All dietary assessment methods engage the cognitive processes of respondents, requiring them to retrieve and report information from memory. I first discuss the distinction between daily and frequency methods of dietary assessment: from a psychological perspective, the essential distinction between these classes of methods is in the cues that are provided for retrieval of information rather than the length of the reference period or the specificity of the information to be retrieved. I then review selectively psychological research on aspects of cognition that are central to dietary reporting; chief among these are the nature of the representation of dietary information in memory and the fidelity of frequency judgments. I conclude by describing several potential areas for collaborative research between cognitive psychologists and nutritional epidemiologists. The ability of respondents to provide data must be considered in the design and selection of dietary assessment methods.