Appendix 7.1 in the APA Publication Manual states that, "[s]ome examples of references and citations to court cases, statutes, and other legislative materials appear in this appendix along with guidelines for their preparation. For more information on preparing these and other kinds of legal references, consult the latest edition of The Bluebook..., which is the source for the legal citation style that follows."
The MLA Style Manual's rule 6.8.14 directs authors to consult The Bluebook as an "indispensable guide," but notes that specific style recommendations "must be adapted to MLA style." This rule provides further direction on how to do so.
AMA Manual of Style rule 3.16 discusses US Legal References and states, "A specific style variation is used for references to legal citations. Because the system of citation used is complex, with numerous variations for different types of sources and among various jurisdictions, only a brief outline can be presented here. For more details, consult The Bluebook: A Uniform System of Citation."
Chicago Manual of Style rule 14.269 states, "Citations in predominantly legal works generally follow one of two guides: (1) The Bluebook...or (2) the ALWD Guide to Legal Citation.... The Bluebook is the most widely used citation guide; its conventions predominate in law reviews. The ALWD Guide differs in some elements and aims to be somewhat simpler. Chicago recommends using one of these systems for citing legal and public documents—including cases, constitutions, statutes, and other government documents—even in works with a predominantly nonlegal subject matter."
This is an updated, online version accessible to users with MSU NetIDs and passwords.
OSCOLA
The Oxford University Standard for Citation of Legal Authorities is a leading style/citation guide for legal materials in the United Kingdom. Wikipedia has a brief description here.