Staffing services provide workers to companies on a temporary or permanent basis. They are contracted or hired by businesses to recruit, train and employ workers. Temporary employment agencies are staffing services that provide workers to businesses on a short-term basis, a long-term basis, or a temporary-to-permanent (temp-to-perm) basis. Providing a short-term temporary employee for a specific project is an important function of a staffing service. As a rule, staffing services provide employers with qualified candidates and are responsible for paying wages, withholding all necessary taxes, and maintaining insurances.

Staffing services provide three types of employees: office and clerical staff, industrial staff, and professional/technical staff. Office and clerical staff make up the largest part of staffing services industry and include administrative assistants, office clerks, and receptionists. Staffing services also provide workers such as laborers, cleaners, and assemblers. In terms of experience, these employees range from inexperienced laborers to highly skilled machine operators. The professional/technical staffing segment covers a wide range of skills and includes engineering temps, engineering contractors, marketing contractors, IT contractors, scientific contractors, healthcare temps, and accountants. An engineering temp or engineering contractor may be hired when, for example, a manufacturer needs engineering support for a project with a fixed duration. In recent years, this practice has proliferated as companies seek to fill short-term, project-based positions while minimizing healthcare costs.

Staffing services can perform the duties of in-house human resources (HR) personnel. For example, hiring employees through a staffing service allows an employer to hire a flexible workforce, add and reduce employees as needed, and reduce the overall cost of employee benefits. Staffing services range in size from international companies to small organizations that focus on specific geographic regions or areas of expertise. For example, IT staffing services may provide programmers, development managers, and systems administrators to government agencies or large-scale manufacturing operations.