Completing questionnaires is a complex task in which multiple cognitive processes play an important role. Despite critiques of the reliability of questionnaires, our research strived to gain more insight into the process of completing questionnaires by using eye-tracking. We investigated how both the question and the categories of answers were being processed and how processing the question influenced the processing of the categories of answers. We also considered the effects of participants' personal characteristics, such as effort and ability. Results showed there were individual differences involved when respondents complete a questionnaire. The respondents spent different amounts of time reading and answering the items, and there were important differences in the quality of processing.