The most common audit report is the unqualified opinion, often referred to as a "clean report". This report indicates that the auditor found the financial statements to be presented fairly and in accordance with GAAP (Generally Accepted Accounting Principles) or other relevant frameworks, with no material misstatements.
The most frequent type of report is referred to as the "Unqualified Opinion", and is regarded by many as the equivalent of a "clean bill of health" to a patient, which has led many to call it the "Clean Opinion", but in reality it is not a clean bill of health, because the Auditor can only provide reasonable assurance ...
There are four types of audit opinions: unqualified, qualified, adverse, and disclaimer of opinion. Each type reflects a different level of assurance and has distinct implications for the audited entity.
Unqualified (clean) audit report
An unqualified opinion is considered a clean report. This is the type of report that auditors give most often. It is also the type of audit report that most companies expect to receive.
Operational. Sometimes called program or performance audits, these are the most common audits. Operating procedures, flow of paperwork, and internal controls are thoroughly reviewed.
The three main types of audits, focusing on who performs them, are Internal Audits (by employees for improvement), External Audits (by independent CPAs for stakeholders), and Government Audits/IRS Audits (by tax authorities). Alternatively, focusing on the purpose, they can be categorized as Financial Audits (financial statements), Compliance Audits (rules/regulations), and Operational Audits (efficiency/effectiveness).
The 5 Cs of audit (Criteria, Condition, Cause, Consequence, Corrective Action) are a framework for structuring clear, actionable audit findings, explaining what should be (Criteria), what is found (Condition), why it happened (Cause), what the impact is (Consequence/Effect), and how to fix it (Corrective Action/Recommendation) to drive organizational improvement and compliance.
The IRS conducts audits by mail or in person. Audits by mail are called “correspondence audits” because they involve document shuffles back and forth between the taxpayer and examiner. Most of the audits conducted by the IRS are correspondence audits. In 2024, 77 percent of audits were by mail.
The four common types of auditors are Internal Auditors (evaluate company operations for management), External Auditors (independent review of financial statements for outside parties), Government Auditors (ensure compliance with laws for public agencies like the IRS), and Forensic Auditors (investigate financial fraud for legal proceedings). These roles focus on different areas, from internal controls and risk management to financial reporting accuracy and fraud detection.
A SOC 2 Type 2 report examines how well a service organization's system and controls perform over a period of time (typically 3-12 months). What is their operating effectiveness? Do they function as intended? Type 2 audits can take 12 months to complete and are more expensive than Type 1 audits.
A successful internal audit function relies on four fundamental pillars, often referred to as the “4 C's”: Competence, Confidentiality, Communication, and Collaboration. These principles guide auditors in delivering meaningful and impactful results.
Key reports are defined as those reports that either develop or assist management in understanding pertinent financial information or serve as a critical component of the control framework.
Typically, you'll need all four: the income statement, the balance sheet, the statement of cash flow, and the statement of owner equity.
Top 10 Audit Firms in the US 2026
Correspondence (Mail) Audit
This is the most common and simplest individual tax audit. The IRS mails a letter (like a CP2000 notice) asking for information on a specific item, such as a missing 1099 or proof of a deduction. Mail audits are narrow, focusing on one or two issues.
The Big 4 are the largest accounting and auditing firms in the world: Deloitte LLP (Deloitte), PricewaterhouseCoopers (PwC), Ernst & Young (EY) and Klynveld Peat Marwick Goerdeler (KPMG).
Big Five
The document outlines the 7 E's—Effectiveness, Efficiency, Economy, Excellence, Ethics, Equity, and Ecology—as essential themes for auditors to enhance organizational success. It emphasizes the importance of incorporating these principles into audit processes to evaluate and improve organizational performance.
Not reporting all of your income is an easy-to-avoid red flag that can lead to an audit. Taking excessive business tax deductions and mixing business and personal expenses can lead to an audit. The IRS mostly audits tax returns of those earning more than $200,000 and corporations with more than $10 million in assets.
The IRS $600 rule refers to a change in reporting requirements for third-party payment apps (like Venmo, PayPal) for taxable income from goods and services, where platforms must send a Form 1099-K if you receive over $600 in a year, intended to capture gig economy/side hustle income, though delays and phased implementation have adjusted the timeline, with current rules for 2024 using a higher threshold ($5,000) before fully phasing to $600 for future years, but remember all taxable income, regardless of form, must always be reported.
The three main types of audits, focusing on who performs them, are Internal Audits (by employees for improvement), External Audits (by independent CPAs for stakeholders), and Government Audits/IRS Audits (by tax authorities). Alternatively, focusing on the purpose, they can be categorized as Financial Audits (financial statements), Compliance Audits (rules/regulations), and Operational Audits (efficiency/effectiveness).
Fundamental Principles Governing an Audit:
There are eight different types of audit evidence. They are physical examinations, confirmations, documentation, analytical procedures, observations, inquiries, reperformance, and recalculation.