You begin fieldwork without a signed engagement letter. Two months later, the CFO disputes the scope and refuses to pay half the fee. Without a signed letter, you have no agreement to enforce.
The engagement letter is the contract that defines what you must do, what management must do, and how disputes resolve. AU-C 210 (Terms of Engagement) makes it mandatory because verbal agreements collapse the moment a controller leaves or a fee dispute surfaces.
HIGH-FREQUENCY: AU-C 210 requires the auditor to agree on terms with management or those charged with governance, document the terms in writing, and obtain agreement (typically a signature) before commencing the audit.
Eight elements must appear in every audit engagement letter. Missing one is a documentation deficiency a peer reviewer will flag.
- Objective and scope. Express an opinion on the financial statements for a specified period. Identify what is being audited.
- Auditor's responsibilities. Conduct the audit under GAAS (or PCAOB standards for issuers). Obtain reasonable assurance that the statements are free from material misstatement. Communicate findings to those charged with governance.
Common mistakes
- Starting fieldwork before the letter is countersigned. The auditor sends October 1, starts October 5, gets a signature October 20. Trap: "fieldwork can proceed as long as the letter was sent." Correct: AU-C 210 requires agreement before commencement; work performed October 5, 20 is a documentation deficiency.
- Issuing a new letter every year for recurring audits. Some candidates over-correct and assume annual letters are mandatory. Trap: "yes, a new letter every year." Correct: the original remains in effect; revise only when a trigger fires.
- Treating an accounting policy change as a framework change. Adopting ASC 606 or ASC 842 is a change within GAAP, not a change of framework. Trap: "the entity adopted ASC 842, so a new engagement letter is required." Correct: framework is unchanged; no letter revision is triggered.
Bottom line
- AU-C 210 requires a written engagement letter signed by both auditor and management before audit work begins.
- Required contents: objective, scope, auditor responsibilities, management responsibilities, framework, report form, fees, and inherent limitations.
- Management responsibilities cover preparing the financials, maintaining internal control, and providing unrestricted access.
- The inherent limitations statement (reasonable, not absolute, assurance) is required and is the auditor's primary legal defense in malpractice claims.
Exam shortcut
When the exam asks "is a new engagement letter required?" run the five-trigger checklist: management/governance change, significant entity change, legal/regulatory change, framework change, terms change. If any trigger fires, revise. If none fires, the original is still in force. Memory aid: MOSAIC for the required contents (Management responsibilities, Objective and scope, Standards and auditor responsibilities, Assurance limitations, Identification of framework, Compensation or fees), plus Other matters and Reporting form.
The full lesson (about 2,227 words, 15 min read) adds 2 worked examples, all 6 common mistakes, a self-check, free in the app.
Learning objectives
- I.D2
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