在英語中，合約一般稱為Contract，協議一般稱為Agreement。

1.何謂“Contract”?

根據法律對contract定義為：A contact in t his Law refers to an agreement establishing, modifying and terminating the civil rights and obligations between subjects of equal footing, that is ,between natural persons, legal persons or other organizations. 根據這一定義，合約平等主體之間設立的確定民事權利和義務的協議。

Steven H. Gifts編著的“Law Dictionary”中將contract 定義為“contract is a promise, or a set of promises, for breach of which the law gives remedy, or the performance of the which the law in some way recognize as a duty.”根據這一定義，合約是一種承諾，違反承諾可以得到法律救助，某種意義上法律將履行該承諾看做是一種補償。

L.B Curzon 在其編撰的字典“A Dictionary of Law”給contract的定義：“Contract is a legally binding agreement”根據這一定義，合約就是有法律約束力的協議。

綜合起來，有一個相同點，就是“Contract is an agreement”，即可將事約說成是“An agreement which binds the parties concerned”或者說成是“An agreement which is enforceable by law”，也可以說：Contracts are promises that the law will enforce。

2. 何謂“Agreement”?

 L.B “A consensus of mind, or evidence of such consensus, in spoke or written form, relating to anything done or to be done.”根據這一定義，協定是對已經做或準備做的相關事宜，經過談判、協商後取得一致意見，以口頭或書面形式做出的約定。

Black “Law Dictionary”有兩個定義。一個是：“A concord of understanding and intention between two or more parties with respect to the effect upon their relative rights and duties, of certain past or future facts or performance”根據這一定義，協定即雙方或多方京某些過去或將來某些事實的相關權利、義務或相關權利、義務的履行而達成的一致理解和願望。

另一個是：The consent of two or more persons concurring respecting the transmission of some property, right or benefits, with the view of contacting an obligation, a mutual obligation.根據這一定義，協定即兩個或多個當事人，為了約定單方責任或相互責任，就財產權利、利益的轉移取得的一致同意。

3. Contract(合約)和Agreement(協議)是不是可以互換呢？

合約的成立必須具備幾個主要因素。它們（要約和承諾構成的）協議、約因、設立法律關係的願望和締約能力四大部分組成。

L.B Curzon編著的“A Diction of Law”提到“Contract generally involves”

1. offer and absolute and unqualified acceptance (要約和絕對接受)

2. consensus ad idem (意思表示一致，也叫meeting of minds)

3. intention to create legal relations (建立合約關係的意願)

4. genuineness of consent (同意的真實性)

5. contractual capacity of the parties (合約當事人的締約能力)

6. legality of object(標的物的合法性)

7. possibility of performance (履行的可能性)

8. certainty of terms(條款的確定性)

9. valuable consideration(等價有償)

Black “Law Dictionary” 中解釋道：Although often used as synonyms with "contract", agreement is a broader term, e.g. an agreement might lack an essential element of a contact." 即“協議”和“合約”經常用作同義詞，但“協議”這一術語含義更廣，例如協議可能缺乏合約的必備條款（essential clauses/provisions）。

實際使用當中，協議可不受必備條款的限制，而稱為合約的文體肯定少不了必備條款，有的合約將其單列，稱為一般條款（General provisions）。

在法律裡規定了八項一般條款，分別是：

1. title or name and domicile of the parities(當事人的名稱或姓名和住址)

2. contract object(標的)

3. quantity(數量)

4. quality(品質)

5. price or remuneration(價款或者報酬)

6. time limit, place and method of performance (履行期限、地點和方式)

7. liability for breach of contract(違約責任)

8. methods to settle disputes (解決爭議的方法)

上述解釋說明，contract(合約)和agreement(協議)的概念雖然接近，但使用範圍不同，不能互換使用。合約是協議的重要組成部分，所有合約一定是協定，而協定不見得都是合約。可以說具備合約成立要求的具有強制執行力的協議才是合約。

結構特點

合約類法律檔用以規定當事人的權利與義務，是預防與解決爭議的依據。

合約英語行文慎密而準確，歷史悠久，深含法律文化底蘊。

中文的合約開頭一般先羅列當事人的名稱、姓名、住所或營業場所，然後是合約正文，結尾是當事人印章、授權代表簽字、職務及簽字日期。

而英語合約一般以下面這類句式為開頭：

This agreement/contract is made and entered in to this ____ day of _____(month), _______ (year) by and between Party A (hereinafter called " Party A ")and Party B(hereinafter called " Party B ")

然後是開始陳述：

WHEREAS...THEREFORE

… It is hereby agreed as follows:

或以：

WITNESSETH, WHEREAS…

NOW THEREFORE, for and in consideration of the mutual covenants and agreements contained herein, the parties hereby covenant and agree as follows:

接著是正文，最後是證明部分，：

IN WITNESS WHEREOF，the parties hereto have hereunto set their hands the day and years first above written.

隨後還包括當事人和見證人的簽字。簽字日期一般在英文合約最搬弄是非是找不到的。