This study aims to: (1) examine the stable and changing components across time of job resources, job demands, work engagement, and burnout, and (2) investigate the relationships --as specified by the Job Demands-Resources model --between job characteristics (demands and resources) and employee well-being (burnout and engagement) when controlled for their stable components. These two issues were addressed using longitudinal data from 3 waves with a 1-year time interval (N = 1,038). Results from structural equation modelling indicate that the stable component accounts for 48-69% (wave 1 to 3) of the total variance in job resources, whereas for job demands these percentages range from 30-35% (wave 1 to 3). Moreover, it appears that 54-66% (wave 1 to 3) of the variance in work engagement and 40-45%(wave 1 to 3) of the variance in burnout is accounted for by a stable component. Hence, compared to the negative aspects of the working environment (i.e., job demands and burnout), positive aspects (i.e., job resources and work engagement) seem to be more stable. We also detected significant relationships between the changing components of job resources and job demands on the one hand and work engagement and burnout on the other. These findings are consistent with the Job Demands-Resources model.