A fee paid to secure special service, especially professional or technical, and to ensure that they are available when needed. Payment for actual services rendered is made separately.

In the legal profession, a retainer is the contract by which a client employs a lawyer, and the lawyer undertakes to perform professional duties and observe fiduciary obligations owed to the client. The retainer is the source of the lawyer’s authority to act on behalf of the client (representing them in Court and outside, with power to bind them in dealings with third parties). At common law, a retainer may be implied from conduct and need not be sourced to a physical document, but rules and regulation of solicitor’s conduct make it effectively mandatory to set out the retainer in writing.