首先我们根据其英文含义去理解，

根据Investopedia上英文含义可知，An engagement letter is a written agreement that describes the business relationship to be entered into by a client and a company. The letter details the scope of the agreement, its terms, and costs. The purpose of an engagement letter is to set expectations on both sides of the agreement.

根据维基百科的英文解释：An engagement letter defines the legal relationship (or engagement) between a professional firm (e.g., law, investment banking, consulting, advisory or accountancy firm) and its client(s). This letter states the terms and conditions of the engagement, principally addressing the scope of the engagement and the terms of compensation for the firm.

"Engagement letter"的直译可以是“聘用函”，但在法律上，它指的是一种合同文件，用于明确和确认律师事务所（或其他专业服务提供者）与客户之间的服务关系。因此，更常见的翻译是“委托函”或“委托协议”。

一般来说，"Engagement letter"中包含了以下信息：

双方身份：明确客户和律师事务所的身份以及法律关系。

服务范围：详细列出律师将提供的具体服务和法律事务的范围。

费用结构：阐明律师费用的支付方式、费率、计费周期以及其他相关费用的安排。

职责和义务：明确双方在服务过程中的职责和义务，包括保密条款、合作方式、信息提供等。

期限和终止：规定服务的起止时间，以及在何种情况下双方可以终止合同。

Engagement letter在法律中的运用是为了确保律师和客户之间的合作关系明确、透明和可靠。它帮助确立律师和客户之间的权益和责任，阐明服务的范围和费用，并规定合同的执行方式和终止条件。这样一来，双方在法律事务中的权利和义务就得到了明确的保障，有助于防止潜在的纠纷和误解的发生。

在法律实践中，Engagement letter通常用于律师、会计师、顾问和其他专业服务提供者与客户之间的合作关系。它是一份重要的文件，双方在合作开始之前通常需要签署以确保双方的权益。

另附一份Engagement letter的Sample供参考：

ENGAGEMENT LETTER

I. THE PARTIES. This Engagement Letter (“Letter”), dated on [DAY] [MONTH], [YEAR], was requested by [NAME] with a mailing address of [ADDRESS], (“Client”) and agrees to hire Service Provider: [NAME] with a mailing address of [ADDRESS] (“Service Provider”).

II. SERVICES PROVIDED. The Service Provider is required to provide the following: [SERVICES] hereinafter known as the “Services.”

III. FEES. For the Services, the Client shall pay the Service Provider: (check one)

☐ – $[AMOUNT] / Hour.

☐ – $[AMOUNT] as a total amount for the Services.

☐ – Other: [AMOUNT]

In addition, the Client may be charged for any administrative fees, filings, or any other costs directly or indirectly related to the Services.

IV. RETAINER. As part of this Letter, the Client agrees: (check one)

☐ – A Retainer Payment is Required. The amount shall be $[AMOUNT] due and payable at the time of signature. The Retainer Payment shall be: (check one)

☐ – Refundable

☐ – Non-Refundable

☐ – A Retainer Payment is Not Required.

V. PRIMARY CONTACT (CLIENT). The primary contact for the Client regarding the Services mentioned in this Letter shall be:

Individual’s Name: [NAME]

Phone: [NUMBER]

E-Mail: [ADDRESS]

VI. TERMINATION. The Services shall terminate: (check one)

☐ – Upon completion of the Services.

☐ – On the end date of [DATE]

☐ – Written notice by either party of [NUMBER] day(s).

☐ – Other. [DETAILS]

The Client shall be required to provide accurate information to the Service Provider in a timely manner. If any information produced by the Client is not accurate the Service Provider shall be held harmless from any legal, financial, or other liability as a result of such information.

IN WITNESS WHEREOF, the Client and Service Provider agree to the terms and conditions contained in this Letter.

Client’s Signature [SIGNATURE] Date [DATE]

Service Provider’s Signature [SIGNATURE] Date [DATE]