Accountancy or accounting is the measurement, statement, or provision of assurance about financial information primarily used by lenders, managers, investors, tax authorities and other decision makers to make resource allocation decisions between and within companies, organizations, and public agencies. The terms derive from the use of financial accounts.

Accounting has been defined by the AICPA as " The art of recording, classifying, and summarizing in a significant manner and in terms of money, transactions and events which are, in part at least, of financial character, and interpreting the results thereof."

Financial accounting is one branch of accounting and historically has involved processes by which financial information about a business is recorded, classified, summarised, interpreted, and communicated; for public companies, this information is generally publicly-accessible. By contrast management accounting information is used within an organization and is usually confidential and accessible only to a small group, mostly decision-makers. Open-book Accounting aims to improve accounting transparency. Tax Accounting is the accounting needed to comply with jurisdictional tax regulations.

Practitioners of accountancy are known as accountants. There are many professional bodies for accountants throughout the world. Many allow their members to use titles indicating their membership or qualification level. Examples are Chartered Certified Accountant (ACCA or FCCA), Chartered Accountant (FCA, CA or ACA), International Accountant (FAIA or AAIA), Management Accountant (ACMA, FCMA or AICWA), Certified Public Accountant (CPA) and Certified General Accountant (CGA or FCGA).

Auditing is a related but separate discipline, with two sub-disciplines: internal auditing and external auditing. External auditing is the process whereby an independent auditor examines an organisation's financial statements and accounting records in order to express an opinion as to the truth and fairness of the financial statements and their adherence to Generally Accepted Accounting Principles (GAAP), or International Financial Reporting Standards (IFRS), in all material respects. Internal auditing aims at providing information for management usage, and is typically carried out by employees of the company.

Accounting scholarship is the academic discipline which studies accounting/accountancy.

Modern accounting

Accounting is the process of identifying, measuring and communicating economic information so a user of the information may make informed economic judgments and decisions based on it.

Accounting is the degree of measurement of financial transactions which are transfers of legal property rights made under contractual relationships. Non-financial transactions are specifically excluded due to conservatism and materiality principles.