This research sought to provide a better understanding of the psychometric multidimensionality of workers’ responses to the Utrecht Work Engagement Scale (UWES; Studies 1 and 3) and the Dutch Work Addiction Scale (DUWAS; Studies 2 and 3). This research also aimed to document the relations between the components of work engagement and workaholism and workers’ functioning (i.e., job satisfaction, work performance, work-family conflict, and sleeping problems). Three studies (N = 273, N = 241, N = 304) were conducted to reach these objectives. Results from these three studies indicated that a bifactor-exploratory structural equation modeling (bifactor-ESEM) representation of workaholism and work engagement ratings was superior to alternative representations. Specifically, employees’ assessments of work engagement concurrently reflected a global work engagement factor which co-existed with specific vigor, dedication, and absorption components. Similarly, employees’ ratings of workaholism revealed a global workaholism factor and simultaneous specific working excessively and working compulsively facets. Our findings also shed light on the criterion-related validity of these workaholism and work engagement components by documenting their differentiated associations with measures of job satisfaction, work performance, work-family conflict, and sleeping problems. Precisely, results from Studies 1 to 3 consistently showed the key role of global workaholism, global work engagement, and the specific vigor facet in predicting outcomes.