To explore the motivational potential of job design, we linked job demands and job resources, as defined in the job demands-resources model, to the motivational process defined in self-determination theory. Specifically, we introduced basic need satisfaction and autonomous motivation as consecutive process variables mediating the relationship between job design and work effort. We tested this model by means of structural equation modeling in a sample of 689 employees. The comparison of several competing models provided support for the hypothesized model. We conclude that job demands thwart and job resources promote the fulfillment of 3 psychological needs. High levels of need satisfaction, in turn, are associated with autonomous motivation and, therefore, with high levels of effort.