Abstract This article outlines a typology of nonresponse biases that may occur in research based on voluntary participation and presents empirical evidence on the relationships between nonresponse and personality traits. We describe four different types of nonresponse occurring at the recruitment stage, during data collection, and at the stage of recruitment for further research. Personality correlates of all types of nonresponse were investigated using data from an online survey e-mailed to owners of personal Web sites, and observer ratings on the targets' personality were obtained. After reviewing the target persons' Web sites, observers judged complete nonrespondents as less agreeable and less open to experience than respondents. Furthermore, higher extraversion, higher openness to experience, and higher narcissism differentiated volunteers for follow-up research from nonvolunteers in both self- and observer ratings. We found only weak evidence of personality correlates of careless and selective item nonresponse. Findings show that nonresponse biases may have significant implications for representativeness in surveys and personality test norms.