Intervene/intervention常用含义为“干涉；介入”，但是在法律领域，其可以表示“参加诉讼；加入诉讼”。

Wikipedia对“intervention”的解释如下：

“In law, intervention is a procedure to allow a nonparty, called intervenor (also spelled intervener) to join ongoing litigation, either as a matter of right or at the discretion of the court, without the permission of the original litigants. The basic rationale for intervention is that a judgment in a particular case may affect the rights of nonparties, who ideally should have the right to be heard.”

也就是说，非诉讼当事方依据法律赋予的权利或经法庭酌情决定后可以加入正在进行的诉讼，而无需获得原当事方的允许，这类非诉讼当事方被称为“参加诉讼人；加入诉讼人”，他们之所以可以加入诉讼是因为案件的判决可能会对他们享有的权利产生影响。

使用时需注意，动词intervene是不及物动词，后面如需搭配名词需使用介词in。

例句：

There are several distinct reasons that someone might wish to intervene in a proceeding:

if the proposed intervenor is currently a litigant in a case with legal issues similar or identical to the case at hand;

if the proposed intervenor represents a group of people who have a direct concern in the legal issues raised in a case (for example, if the case involves deportation of a particular individual, an application for leave to intervene might be made by an interest group for the rights of refugee claimants);

if the proposed intervenor is concerned that the court's decision in a particular case might be so broad as to affect the proposed intervenor's interests; in other words it would be an intervention to ensure that the court's ruling does not have unintended consequences.（来源：Wikipedia）

希望加入诉讼或许基于以下原因：

拟加入诉讼人目前为某一案件的诉讼当事方，而该案件所涉法律问题正好与拟加入诉讼类似或相同；

拟加入诉讼人是与案件所涉法律问题有直接关系的群体代表（比如，如果案件涉及递解某一特定人士出境，那么相关利益团体可能会为难民申请人争取权利而申请加入诉讼许可）；

拟加入诉讼人担心法院针对特定案件所作裁决可能过于宽泛，从而影响其自身权益；换句话说，只有加入诉讼才能确保法院的裁决不会产生意外后果。

此外，leave to intervene表示“加入诉讼许可”，motion to intervene表示“加入诉讼申请”。

例句1：

A petition for leave to intervene may be filed in any proceeding before the Administration. The petition will be granted by the presiding officer if the proposed intervenor establishes that it has a substantial interest in the proceeding and will not unduly broaden the issues therein or unduly delay the proceeding. All such petitions shall be filed prior to the opening of the prehearing conference, or if none is held, before the commencement of hearing, unless petitioner shows good cause for allowing the petition at a later time. Intervention petitions shall be served in the same manner as other petitions, and shall be subject to answer. Intervention petitions will be granted where necessary to protect substantial interests of the petitioner and where intervention will not materially broaden the issues. A person granted permission to intervene becomes a party to the proceeding.（来源：46 CFR § 201.78）

任何法律程序均可向管理部门提交加入诉讼许可申请书。若拟加入诉讼人可以证明其与诉讼存在实际利害关系，且不会不当扩大所涉问题或延误诉讼，则审裁官予以批准。所有申请须于预审会晤之前提交，若无预审会晤，则须于听证会开始前提交，除非申请人有正当理由延迟提交申请。加入诉讼申请的送达方式与其他申请一样，且须随附答辩状。加入诉讼申请会在必要时予以批准用以保护申请人的实际利益，且须保证加入诉讼实质上不会扩大所涉问题。获准加入诉讼的一方成为诉讼当事方。

例句2：

A motion to intervene must be served on the parties as provided in Rule 5. The motion must state the grounds for intervention and be accompanied by a pleading that sets out the claim or defense for which intervention is sought.（来源：Rule 24, Federal Rules of Civil Procedure）

加入诉讼申请须按照规则5的要求向各当事方送达。申请须注明加入诉讼的原因，并随附载明加入诉讼所涉索赔或答辩的诉讼文件。