The general definition of an audit is an evaluation of a person, organization, system, process, project or product. Audits are performed to ascertain the validity and reliability of information; also to provide an assessment of a system's internal control. The goal of an audit is to express an opinion on the person/organization/system (etc) in question, under evaluation based on work done on a test basis. Due to practical constraints, an audit seeks to provide only reasonable assurance that the statements are free from material error. Hence, statistical sampling is often adopted in audits. In the case of financial audits, a set of financial statements are said to be true and fair when they are free of material misstatements - a concept influenced by both quantitative and qualitative factors.

Traditionally, audits were mainly associated with gaining information about financial systems and the financial records of a company or a business (see financial audit). However, recent auditing has begun to include other information about the system, such as information about environmental performance. As a result, there are now professions conducting environmental audits.

In financial accounting, an audit is an independent assessment of the fairness by which a company's financial statements are presented by its management. It is performed by competent, independent and objective person(s) known as auditors or accountants, who then issue an auditor's report based on the results of the audit.

Such systems must adhere to generally accepted standards set by governing bodies regulating businesses; these standards simply provide assurance for third parties or external users that such statements present a company's financial condition and results of operations 'fairly'.

Quality audits

Main: Quality audit

Quality audits are performed to verify the effectiveness of a quality management system. This is part of certifications such as ISO 9001. Quality audits are essential to verify the existence of objective evidence of processes, to assess how successfully processes have been implemented, for judging the effectiveness of achieving any defined target levels, providing evidence concerning reduction and elimination of problem areas and are a hands-on management tool for achieving continual improvement in an organization.

To benefit the organization, quality auditing should not only report non-conformances and corrective actions but also highlight areas of good practice. In this way, other departments may share information and amend their working practices as a result, also enhancing continual improvement.

Integrated audits

In the US, audits of publicly-listed companies are governed by rules laid down by the Public Company Accounting Oversight Board (PCAOB). Such an audit is called an Integrated Audit, where auditors have the additional responsibilities of expressing opinions on the management's assessment of the firm's internal control and the effectiveness of internal control over financial reporting, based on their (the auditors') own assessment.