This article contributes to the growing research interest on sustainability-directed citizenship behaviors by helping to develop the construct of organizational citizenship behaviors (OCBs) toward the environment, defined as voluntary behavior not specified in official job descriptions that, through the combined efforts of individual employees, help to make the organization and/or society more sustainable. Hypotheses predict the extent to which employees' beliefs about their organization and about sustainability in general will be associated with OCBs toward the environment. The hypotheses are tested via a field survey of 733 employees working in a variety of occupations. Regression results indicated that OCBs toward the environment were related to, yet distinct from, OCBs in general, perceived organizational support (POS), affective commitment (AC), and beliefs that sustainability is important both in general and for one's current organization. The article concludes with theoretical implications for research on sustainability and extra-role behaviors as well as the practical implications for managers wishing to foster sustainability in their organization.