Although driving automation can relieve the driver of some driving tasks, it can also introduce new driving tasks. Unless driving automation is at SAE Level 5, drivers are expected to be fit to resume vehicle control either when they detect a need for it or when they are handed over vehicle control by automation. Just as in non-automated driving, driver’s situation awareness and performance of the automated driving task may be affected by different types of driver impairment. This chapter presents four major impaired states that can degrade driver’s fitness to resume vehicle control: distraction, sleepiness, impairment from alcohol and other drugs, and motion sickness. The sources, effects, detection and prediction, and remediation of these four impaired states within the driving automation context are covered. In general, the impairments discussed in this chapter have a wide variety of shared and unique effects, reflect characteristic mechanisms of onset, intensity, and duration, and can interact in complex ways. Importantly, impairment effects may become more prevalent with the introduction of higher levels of driving automation, thereby potentially reducing safety benefits of higher automation levels. The chapter highlights some of the challenges of defining, detecting and predicting, and remediating these impairments, and proposes directions for future research.