There is general agreement that the world of work has changed considerably over the past decades. The levels at which transformations are taking place range from the macro-level of economies to the micro-level of work tasks. At the macro-level, globalization, the continuing shift away from manufacturing toward services (postindustrialization; Bell, 1973), and rapid technological advances (Rosa, 2003) are but a few current trends. At the meso-level of organizations, we are witnessing the implementation of new management practices and decentralized, flexible organizational structures (Cascio, 2003). These economic and organizational changes inevitably alter what is expected of workers and bring about new demands at the micro-level of work tasks. Among these new demands are increasing pressures to work at high speed (Green, 2004), to plan, structure, and control work activities autonomously (Pongratz & Vos, 2003), to acquire new knowledge and skills (Loon & Casimir, 2007), and to deal with rising job insecurity (Blossfeld, Mills, Klijzing, & Kurz, 2005). Despite the increasing awareness of the emergence of new job demands among researchers and practitioners, only a few theoretical and empirical works have so far examined these new job demands and their impact on employees’ well-being and performance (e.g., Obschonka, Silbereisen, & Wasilewski, 2012). Moreover, current transformations in the world of work seem to warrant a reconsideration of traditional approaches to job demands. Firstly, job demands emanating from current economic and organizational changes challenge the binary logic of distinguishing between either positive (i.e., job resources) or negative job characteristics (i.e., job demands), as suggested by various theoretical models (e.g., job demands-resources model, Bakker & Demerouti, 2007). The need to acquire new knowledge and skills, for example, fits neither into existing conceptualizations of job demands as hindering personal development and impairing employee health nor into existing conceptualizations of job resources as exclusively positive aspects of one’s job. Rather, the acquisition of knowledge and skills is both potentially positive and stressful, since it enables personal development and concurrently consumes cognitive and temporal resources. The challengehindrance approach to job stressors (e.g., LePine, Podsakoff, & LePine, 2005) offers the opportunity to simultaneously consider positive and negative aspects of job demands by differentiating between job challenges and job hindrances. According to this approach, job hindrances impair both well-being and motivation; whereas job challenges are, despite their potentially stressful nature, positive for individual motivation and performance. Combining the job demands-resources model and the challenge-hindrance approach in order to distinguish between job resources, job challenges, and job hindrances (Van den Broeck, De Cuyper, & De Witte, 2010) and their differential relations to well-being seems to be a promising avenue to take into account the ambivalent (i.e., simultaneously positive and negative) consequences of job demands emanating from economic and organizational changes. Secondly, demands emanating from economic and organizational changes challenge the assumption that job characteristics have generally linear relations with outcome variables. For example, the demands to plan, structure, and control work activities autonomously (Pongratz & Vos, 2003) and to acquire new knowledge and skills (Loon & Casimir, 2007) may only be beneficial up to a certain level and may become stressful or harmful thereafter (e.g., Kubicek, Korunka, & Tement, in press). Warr’s (1994) vitamin model tries to describe such curvilinear relations by drawing an analogy to the effects of vitamins on a person’s health. More precisely, Warr (1994, p. 88) states that ‘‘the intake of vitamins is important for physical health up to, but not beyond, a certain level’’ and that in case of some vitamins (i.e., vitamin A or D) excessive consumption can even be harmful. Certain features of the work environment are proposed to have similar properties as these vitamins, such that after a certain point, an increase in beneficial job characteristics may not have a beneficial