With the demographic changes in our modern societies and the economic pressures to reform the welfare state, volunteer work to provide social services has increased in importance. From several studies we know, however, that work for volunteer organizations is in decline. Thus, the question of "what motivates volunteers?" will gain in importance over time. While a series of studies has already addressed this question by using surveys and experiments, we still fail to have ?rm knowledge of the motivation of volunteers. More precisely, recent work suggests that volunteer work can be stimulated most successfully if incentives o?ered to volunteers are tailored to the latter's initial motivation in joining a volunteer organization. Studies employing surveys of volunteers can, however, because of problems of self-selection, hardly yield de?nite conclusions on the varying e?ects of incentives o?ered to volunteers. Similarly, they fail to allow for studying the long term e?ects of motivations and incentives. Lab experiments, on the other hand, often su?er from a lack of external validity. The goal of the proposed research project is to gain a ?rmer understanding how motivations and incentives for volunteer work interact. Of crucial interest ? Institute for Political Science (IPZ), University of Zurich, Hirschengraben 56, 8001 Zurich, Switzerland. Phone +41 (0)44 , 634 50 90 email: email@example.com 1 will be the question, what role egotistical and altruistic motivations play during the recruitment process and long term in a volunteer's career. The use of a ?eld experiment in collaboration with volunteer organizations will allow us to overcome the shortcomings of existing work. In this ?eld experiment, we ?rst wish to assess the e?ect of persuasive motivational messages on potential volunteers. In a second step, selective incentives will be used in order to test their e?ect on volunteer commitment and volunteer satisfaction. Parallel to the ?eld experiment, a lab experiment will be conducted in order to reduce possible motivational bias due to the exposure to persuasive messages prior to motivational assessment. Given the experimental setting we will be able to precisely trace the e?ect of incentives on volunteer work and follow also the induced changes in motivations. The insights gained will not only close an important gap in the literature, but also be of practical value to third sector organizations in order recruit and retain volunteers.