At-will employment is a legal doctrine in the United States that allows employers to terminate an employee at any time, with or without notice or cause, as long as the reason is lawful. Likewise, employees may resign at any time without providing notice. 

While at-will employment offers flexibility for employers, it does not override worker protections against unlawful termination, such as discrimination, retaliation, or violations of employment contracts. Certain exceptions apply, including unionized workers or employees covered by specific agreements. Critics argue that at-will employment can limit job security for employees despite its legal safeguards.