ADP is a provider of payroll and human capital management solutions servicing the full scope of businesses from micro to global enterprises. ADP was established in 1949 and serves over 1 million clients primarily in the United States. ADP's employer services segment offers payroll, human capital management solutions, human resources outsourcing, insurance and retirement services. The smaller but faster-growing professional employer organization segment provides HR outsourcing solutions to small and midsize businesses through a co-employment model.