This study investigates the social–psychological mechanisms leading individuals in organizations to engage in environmental citizenship behaviors, which entail keeping abreast of, and participating in, the environmental affairs of a company. Informed by the corporate greening and organizational behavior literature, we suggested that an employee’s level of involvement in the management of a company’s environmental impact was the overt manifestation of his or her discretionary sense of commitment to environmental concerns in the work context, and that such commitment developed through the interplay of individual, organizational, and supervisory factors. Our general findings support the idea that when environmental protection is valued and encouraged by the company and line managers, organization members are more likely to experience a volitional sense of attachment and responsibility to corporate environmental goals and values, which is enacted through citizenship behaviors. We also expected that individual ecological beliefs would strengthen the environmental commitment of employees via identification with, and adherence to, the socially responsible cause embodied by the organization and its managerial staff. But it did not. On the contrary, the data indicated that corporate environmental policy is more likely to influence an employee’s level of environmental commitment when he or she holds weak versus strong personal ecological beliefs. Theoretical and managerial implications of our findings are discussed.