This document provides an overview of human resource outsourcing. It defines human resources, outsourcing, and human resource outsourcing. It discusses the history of outsourcing and categories of human resource outsourcing such as professional employer organizations, business process outsourcing, and application service providers. Trends in human resource outsourcing are also examined, such as a growing focus on cost savings and expertise rather than just cost savings alone. Hybrid models that use a mix of in-house and outsourced human resource functions are becoming more common.