An attest service, or attestation service, is an independent review of a company's financial statement conducted by a certified public accountant (CPA). The CPA delivers an attestation report with conclusions about the reliability of the data.    Auditing is a subset of attestation engagements. It is a more comprehensive examination of a company's financial statements. It includes not only an assessment of whether or not the statements are accurate, but also an evaluation of the company's internal controls and accounting procedures.