This article puts forward the case that survey questionnaires, which are a type of measuring instrument, can and should be tested to ensure they meet their purpose. Traditionally survey researchers have been pre-occupied with 'standardising' data collection instruments and procedures such as question wording and have assumed that experience in questionnaire design, coupled with pilot testing of questionnaires, will then ensure valid and reliable results. However, implicit in the notion of standardisation are the assumptions that respondents are able to understand the questions being asked, that questions are understood in the same way by all respondents, and that respondents are willing and able to answer such questions. The development of cognitive question testing methods has provided social researchers with a number of theories and tools to test these assumptions, and to develop better survey instruments and questionnaires. This paper describes some of these theories and tools, and argues that cognitive testing should be a standard part of the development process of any survey instrument.