The reason for the popularity of the questionnaire lies in its cost, time efficiency, and anonymity. The number of participants to which a questionnaire can reach out (i.e., its breadth) makes up for its potential lack of depth in investigating issues which are offered by other techniques, such as multiple interviews or observations. This chapter provides an introduction to questionnaire development and questionnaire analyses for language assessment use and research purposes. The premise of this chapter is that if researchers are to use a questionnaire for a particular assessment or research purpose appropriately, they ought to know what it can and cannot do. The chapter first discusses contexts in which questionnaires can be used to elicit information from test takers, students, research participants, or other stakeholders. It then presents the limitations of questionnaires. The typical stages in questionnaire development and use are outlined, followed by essential skills and strategies for constructing and analyzing a questionnaire. Selected examples of questionnaires in published research are then discussed.