Since 1994, the German Mobility Panel (MOP) has been one of the oldest multiday and multiperiod travel surveys. Along with the need to understand behavioral processes, the demand for such detailed and extensive data is increasing. However, for respondents to take part in a survey like the MOP is often time-consuming. Therefore, with generally declining response rates, it is even more difficult to recruit a suitable sample of test participants for a multiday or multiperiod survey. If a selective nonresponse problem exists, this calls into question the representativeness of such a survey. For the MOP, respondents were recruited in a multistage process that provided an opportunity to study selectivity. The findings indicate that sociodemographics dominate selective nonresponse. There is also some mobility-related selectivity because people for whom mobility is an everyday issue take a stronger interest in the survey topic and are therefore more likely to participate in the survey. It was also found that recruiting households instead of individuals is advantageous because it partly remedies selectivity problems. In addition, the study produced insight about the reliability and trustworthiness of computer-assisted telephone interview data and how they should be interpreted.