Because of the declining penetration rate of landline telephones and a general decline in the willingness to participate in surveys conducted through traditional data collection modes, survey data collection using online methods–especially online panels–is becoming more popular worldwide. Although these surveys have been widely adopted among marketing researchers, critics still fear that this sampling method leads to biased results produced by a breed of “expert” volunteer survey respondents who are solely interested in monetary incentives and therefore cannot be compared with the general population. This chapter first gives an overview of the existing literature on motives for participating in surveys in general and online panels in particular and how these motives influence survey participation behavior in the panel. Then, a new study among 1,612 members of an Austrian nonprobability online panel is presented. The results show that although other reasons for becoming an online panel member, such as helping to develop better products and services or entertainment, are reported more often, respondents who said that they joined the panel because of the promised monetary incentives have a higher starting and a lower break-off rate than do those who cited intrinsic reasons. Additionally, other characteristics of online panel members like the time of panel entry (panel tenure) and how they were recruited to the online panel, seem to be at least as important as monetary motives in determining survey participation behavior in online panels.