Every business that registers with HMRC as an employer gets an employer PAYE reference number (or, simply, PAYE number). It's also known as an Employer Reference Number (ERN).
Your PAYE number is made up of two parts – a three-digit HMRC office number, and a reference number unique to your business. It’ll usually look something like 123/A45678 or 123/AB45678 (although there can be exceptions).
Read our guide to PAYE numbers for more information.