This article describes the models and methods that cognitive psychologists and survey researchers use to evaluate and experimentally test cognitive issues in questionnaire design and subsequently improve self-report instruments. These models and methods assess the cognitive processes underlying how respondents comprehend and generate answers to self-report questions. Cognitive processing models are briefly described. Non-experimental methods--expert cognitive review, cognitive task analysis, focus groups, and cognitive interviews--are described. Examples are provided of how these methods were effectively used to identify cognitive self-report issues. Experimental methods--cognitive laboratory experiments, field tests, and experiments embedded in field surveys--are described. Examples are provided of: (a) how laboratory experiments were designed to test the capability and accuracy of respondents in performing the cognitive tasks required to answer self-report questions, (b) how a field experiment was conducted in which a cognitively designed questionnaire was effectively tested against the original questionnaire, and (c) how a cognitive experiment embedded in a field survey was conducted to test cognitive predictions.