Self-reports of behaviors and attitudes are strongly influenced by features of the research instrument, including question wording, format, and context. Recent research has addressed the underlying cognitive and communicative processes, which are systematic and increasingly well-understood. The author reviews what has been learned, focusing on issues of question comprehension, behavioral frequency reports, and the emergence of context effect in attitude measurement. The accumulating knowledge about the processes underlying self-reports promises to improve the questionnaire design and data quality.