ADP is one of the world's largest providers of payroll and human capital management (HCM) technology and services. Founded in 1949 as a manual payroll bureau in New Jersey, it now runs cloud-based platforms that pay and manage the workforces of more than a million clients across 140 countries, processing pay for roughly 42 million workers. Its business spans payroll, tax filing, benefits, talent, time and attendance, retirement services, and full HR outsourcing through its PEO arm.
Paychex is a Rochester, New York-based provider of payroll, human resources, retirement and insurance services for small and medium-sized businesses. Founded in 1971 by Tom Golisano with $3,000, it has grown into a Fortune 500 company that pays roughly 1 in 11 U.S. private-sector workers and now embeds AI across its platforms following its 2025 acquisition of Paycor.