In the United States, at-will employment defines a working relationship in which either party can break the employment agreement without liability. This doctrine assumes there was no explicit contract between the employer and employee and that the employer does not belong to a union. The document officially states "the employer is free to discharge individuals "for good cause, or bad cause, or no cause at all," and the employee is equally free to quit, strike, or otherwise cease work."

This policy theoretically reduces job security, as employers can terminate a position for any reason, or even no reason at all. A company is free to fire workers en masse if diminishing profits began to eat away at the employer's sustainability. Other negative behaviors, such as workplace bullying, can occur because of the influence of an environment of fear and job insecurity created by at-will employment.

However, several exceptions to the at-will doctrine do exist. Blatant, unlawful discrimination against employees because of factors such as age, race, religion, national origin, pregnancy, or disability status resulting in termination is prohibited under the doctrine. If an employee was let go because of one of these reasons, wrongful termination lawsuits may result for the employer. Other reasons a company may not fire an at-will employee include refusing to commit illegal actions, family or medical leave, and not following the stated termination procedures. Most employers have an explicit method of firing workers, outlined in a company handbook or manual. If these steps are not followed, a wrongful termination case may be in store.

The idea of at-will employment originated in Horace Gray Wood's 1877 discourse on master-servant relations. His idea proposed it was slaves' responsibility to prove an express contact existed between master and slave. From this point, the concept of employee discharge without a reason and at-will employment was born. This rule was initially adopted by all U.S. states. It was not until 1959 that the first legal exception to the idea of at-will employment was created. Since that point in history, more exceptions and technicalities have added to the law, although the burden of proving wrongful termination still rests with the employee. Protective laws for employees include the Equal Pay Act of 1963, the Age Discrimination in Employment Act of 1967, and the Americans with Disabilities Act of 1990.