Most employees are covered by workers' compensation because their employers are required to pay for insurance. However, in some states, only employers with a certain amount of employees must have workers' comp insurance. Also, most injuries that happen at work or because of work are covered under workers' comp, regardless of who was at fault. Work-related injuries can either be one-time events or illnesses that developed over time, such as repetitive stress injuries.

Some injuries that happen at work may or may not be covered by workers' compensation; these include injuries due to drug or alcohol use, injuries caused by fighting or self-infliction, injuries that happen while committing a crime, and psychiatric injuries.