In this chapter, we focus on the questionnaire as the main instrument in survey research. We start by discussing the foundation of all questionnaires-the actual questions. We look at the content of questions; differentiate between closed-ended, open-ended, and contingency-type questions; and analyze their format and sequencing. Next we explore possible biases in the wording of questions, as well as leading, double-barreled, and threatening questions. Finally, we give important pointers about the cover letter accompanying the questionnaire and the instructions included in it.