Automatic Data Processing (ADP) runs payroll and HR administration software for businesses of all sizes — from small businesses to large enterprises — across 140 countries. Employers pay ADP to handle payroll processing, tax compliance, benefits administration, talent management, and retirement services. ADP also offers a Professional Employer Organization (PEO) service, where it co-employs client workers and takes on HR, benefits, and compliance responsibilities directly. Revenue comes from software subscription fees and per-employee-per-month service fees, plus ADP earns float income on client funds held temporarily before payroll is disbursed. With 1.1 million clients and payroll processed for over 42 million workers, scale is central to the business model.