In long, stressful operational periods, military personnel face numerous challenges that may compromise their performance, an especially important one being fatigue. Current literature supports the view that behavioral, physiological, and cognitive factors are all predictive of the level of fatigue in individuals. However, much of the work on modeling fatigue has taken a narrow approach, relying only on a handful of modalities to measure fatigue. This paper aims to fill the void by providing an extensive overview of the current literature on both computationally measuring and modeling fatigue. We provide up-to-date and practical advice on which models are best suited for different situations and highlight directions for future work.