An accounting audit firm is a professional services company that specializes in providing assurance services to businesses, organizations and other entities. These services include financial statement audits, reviews, and compilations, internal control assessments, and agreed-upon procedures.

An accounting audit firm employ trained and licensed professionals, such as certified public accountants (CPAs), to provide these services to their clients. They work to ensure that the financial statements of their clients are accurate, complete, and in compliance with Generally Accepted Accounting Principles (GAAP) or international Financial Reporting Standards (IFRS).

The main purpose of an accounting audit firm is to provide an independent assessment of an organization's financial statements. Through an audit, the firm examines the financial records and transactions of the entity, and provides a report on the fairness and accuracy of the financial statements. The aim is to give assurance to the stakeholders of the organization that the financial statements are free of material misstatements, whether caused by fraud or error.

Audits are often required by laws or regulations and stakeholders such as banks, investors, and regulatory bodies. The auditor, who is independent from the organization, performs the audit and express an opinion on whether the financial statements are presented fairly in all material respects.

In addition to financial statement audits, accounting audit firms may also provide a range of other services such as review of financial statement which is a less extensive examination than an audit, and compilation which is preparing financial statements based on information provided by management without an examination.

Accounting audit firms also perform internal control assessments, which evaluate the system of internal controls in place to ensure that financial reporting is accurate and reliable. They also perform agreed-upon procedures engagements which the client and the firm agree on specific procedures to be performed by the firm and the results are reported to the client, but no opinion is expressed.

Overall, an accounting audit firm plays a vital role in ensuring the accuracy and reliability of financial information, and helping organizations comply with financial and regulatory requirements.