From Ken Strutin’s introduction to this guide: In the legal system, such intonements have taken on the form of specialized briefs called amicus curiae (“friend of the court”). And through extension and by complement they have appeared in the form of law reviews, media articles, exposes, and books. Indeed, there is an oscillating relationship between amici and law reviews, which has been beneficial for scholarship and public discourse. In the end, it is the passion for justice that drives individuals, governments, academics, lawyers, journalists and other interested groups to befriend the courts. The amicus has the power to speak to many audiences simultaneously. In the courtroom, it is the honest broker; in the public media, it is the educator; in academia, it is scholarly analysis and historical perspective. Bounded by common law, court rules, and the conventions of publishing (briefs, articles or books), the amicus can yet move knowledge into venues where it is most needed. An amicus can serve as an “oral shepardizer,” expert witness, or quasi-litigant that extends the range of judicial notice and culls, concentrates and vets information into a case-specific resource. Still, there is a tension between the role of the amicus as independent expert offering facts and a party arguing an agenda, which can ultimately impact the quality and constitutionality of decision-making. Indeed, there are concerns that unregulated amicus practice can undermine development of case law by opening the door to issues and arguments beyond the threshold of standing and jurisdiction. Lastly, the free range of amicus briefs can exacerbate already problematic judicial information seeking behavior. Roman legal tradition fashioned the amicus into an interlocutor, an explainer in all kinds of cases. Today, their roles are circumscribed by court rule and common law. However, the scope of this article is confined to a discrete precinct of the amicus universe, criminal justice.