Title. Internet-based instructor-led mindfulness for work-related rumination, fatigue and sleep: assessing facets of mindfulness as mechanisms of change. A randomised waitlist control trial.Abstract. This study aimed to extend our theoretical understanding of how mindfulnessbased interventions exert their positive influence on measures of occupational health.Employing a randomised waitlist control study design, we sought to: (1) assess an Internetbased instructor-led mindfulness intervention for its effect on key factors associated with 'recovery from work', specifically, work-related rumination, fatigue and sleep quality; (2) assess different facets of mindfulness (acting with awareness, describing, non-judging, and non-reacting) as mechanisms of change; and (3) assess whether the effect of the intervention was maintained over time by following up our participants after three and six months.Participants who completed the mindfulness intervention (N=60) reported significantly lower levels of work-related rumination and fatigue, and significantly higher levels of sleep quality, when compared with waitlist control participants (N=58). Effects of the intervention were maintained at three and six month follow-up with medium to large effect sizes. The effect of the intervention was primarily explained by increased levels of only one facet of mindfulness (acting with awareness). This study provides support for online mindfulness interventions to aid recovery from work and furthers our understanding with regards to how mindfulness interventions exert their positive effects.