Assurance service is an independent professional service, typically provided by Chartered or Certified Public Accountants or Chartered Certified Accountant, with the goal of improving information or the context of information so that decision makers can make more informed, and presumably better, decisions. Assurance services provide independent and professional opinions that reduce information risk (risk from incorrect information).

Audits are therefore a type of assurance service. However, audits only test the validity of the assertions in financial statements, and are subject to regulation under International Standards on Auditing. Assurance engagements designed to test historical financial information are referred to as assurance reviews (these are regulated by International Standard on Review Engagements (ISRE 2400)), but assurance reports can be obtained over many other subject matters and will then be subject to ISAE 3000 or other individual Standards on Assurance Engagements.