美国Code of Federal Regulations分别对“intervenor”和“amicus curiae”作出了如下规定：

“Intervenors are organizations or persons who want to participate in a proceeding because they believe the proceeding, or its outcome, may affect their rights or duties. Intervenors as a “matter of right” are those parties who have a statutory right to participate. “Permissive” intervenors are those parties who may be permitted to participate if the proceeding will affect them directly and if intervention is otherwise appropriate under law. A request to intervene may be made by motion filed with the judge.

Intervenors have the same rights and duties as parties, with the following two exceptions:

(1) Intervenors do not have an independent right to a hearing; and

(2) Permissive intervenors may participate only on the issues affecting them. The judge is responsible for determining the issues on which permissive intervenors may participate.

An amicus curiae is a person or organization who, although not a party to an appeal, gives advice or suggestions by filing a brief with the judge or the Board regarding an appeal. Any person or organization, including those who do not qualify as intervenors, may request permission to file an amicus brief. The Board may solicit amicus briefs on its own motion.

A request to file an amicus curiae brief must include a statement of the person’s or organization’s interest in the appeal and how the brief will be relevant to the issues involved.

The request may be granted, in the discretion of the judge or the Board, if the person or organization has a legitimate interest in the proceedings, and such participation will not unduly delay the outcome and may contribute materially to the proper disposition thereof.

The amicus curiae shall submit its brief within the time limits set by the judge or the Board and must comply with any further orders by the judge or the Board.

An amicus curiae is not a party to the proceeding and may not participate in any way in the conduct of the hearing, including the presentation of evidence or the examination of witness. The Board, in its discretion, may invite an amicus curiae to participate in oral argument in proceedings in which oral argument is scheduled.”

大致意思是，“intervenor”是指因其认为诉讼或诉讼结果可能会对自身权利或义务产生影响而希望参与诉讼的组织或个人。无论是依据法律有权参与诉讼还是法律许可参与诉讼，可向法官提出申请。需要注意的是，“intervenor”不享有独立的听证权；并且，许可参与诉讼的“intervenor”只能参与对其有影响的诉讼。而“amicus curiae”是指通过向法官递交意见陈述书就诉讼提出建议的非当事方个人或组织。任何人或组织（包括无资格作为intervenor的个人或组织）都可向法官请求递交非当事方意见陈述书，该陈述书须表明该人或组织与诉讼的利益关系以及陈述书与诉讼的相关性。如果该人或组织与诉讼存在合法的利益关系，且其参与诉讼不会不适当地导致结果延迟，则法官可能会予以批准。由于“amicus curiae”并非诉讼当事方，其不得参与听审，包括不得举证，不得讯问证人。

例句1：

The Secretary for Justice (“SJ”) was granted leave to intervene in the present proceedings. To avoid any potential prejudice to SJ’s prosecutorial function under Article 63 of the Basic Law (“BL 63”), SJ’s involvement was limited to submissions on questions of broad public policy, which did not necessitate examination into specific details of the Proposed Funding Arrangement. In the circumstances, the Court appointed amicus curiae to assist on all relevant issues.（来源：https://www.doj.gov.hk/en/notable_judgments/pdf/HCMP_2728_2017e.pdf）

律政司司长获准参与当前法律程序。为避免对《基本法》第63条所述律政司司长的检察职能造成任何潜在损害，律政司司长仅能针对广泛的公共政策相关问题提供意见，不会涉及拟议出资安排的具体情况。在这种情况下，法院委任法庭之友协助处理相关所有问题。

例句2：

In a utility rate case, the original parties are the applicant utility and the Commission’s Utilities Division (“Staff”). Sometimes a utility customer whose budget would be significantly affected by the rates proposed in the application desires to present the Commission evidence specifically related to the impact that the rates would have on the customer. To be able to do this, the customer would need to request and be granted intervention, which would make the customer a party to the case—an intervenor. Like the utility and Staff, an intervenor can provide evidence and cross-examine other parties’ witnesses.（来源：https://www.azcc.gov/docs/default-source/hearings-files/intervention-final43b78e44d05e491e99f0c25bf8928f1f.pdf?sfvrsn=2436fd2b_9）

在公用事业费相关案件中，原当事方包括申请人公用事业单位和委员会公用事业部门（“管理人”）。有时，由于公用事业客户的预算会在很大程度上受拟议费率的影响，其欲向委员会提交有关费率对其产生影响的证据。为此，该客户需要提交参与讼诉申请，获批后即成为案件当事方——参与诉讼人。与公用事业单位和管理人一样，参与诉讼人可以提供证据，交叉询问其他当事方的证人。