An Employee Identification Number (EIN) is a unique identifier assigned to employees by their employer. This number is used for various purposes, including payroll processing, tax reporting, and maintaining employee records. It helps ensure accurate tracking of an employee's work history and earnings. The EIN is often required when filling out tax forms, such as W-2 forms, which report an employee's annual wages to the Internal Revenue Service (IRS). Employers use this number to differentiate between employees and manage their payroll efficiently, ensuring compliance with tax regulations.