A professional employer organization (PEO) is an organization that enters into a joint-employment relationship with an employer by leasing employees to the employer, thereby allowing the PEO to share and manage many employee-related responsibilities and liabilities. This allows employers to outsource their human resource functions, such as employee benefits, compensation and payroll administration, workers' compensation, and employment taxes.

PEOs typically serve as a professional employer of their clients' employees. The client company reports its wages under the PEO's federal employer identification number (FEIN), and employee liability shifts to the PEO. Employers gain economies of scale by having more benefits options, sometimes at lower rates.