An amicus curiae brief, Latin for 'friend of the court,' is a legal filing submitted by an entity that is not a direct party to a lawsuit but has a strong interest in its outcome or can offer relevant expertise. Courts are not required to accept amicus briefs but routinely do so in cases involving significant public policy questions. In the Anthropic v. Pentagon case, Microsoft filed an amicus brief warning of 'broad negative ramifications' from the supply chain risk designation, and 22 retired senior military officials filed a separate brief arguing that Hegseth's action represents 'the misuse of powerful national security authorities by civilian political leadership.' Both groups argued that the case raises issues that extend far beyond the two specific parties in the lawsuit.