What citation format ( bluebook, Chicago, etc) does the Ninth Circuit Court of Appeals use/require/prefer?

Majority of federal courts, including I believe the Ninth Circuit, utilizes the bluebook format. See references below for general information: http://lawweb.usc.edu/library/research/location/citations.cfm http://en.wikipedia.org/wiki/Bluebook http://www.ca9.uscourts.gov/content/view.php?pk_id=0000000379

According to the "Bible" for Ninth Circuit Appeals: "The Ninth Circuit has not adopted a particular 'style manual' for use in citing legal authorities in briefs filed before it. The current edition of the 'Harvard Blue Book' (A Uniform System of Citation) is recommended; but any accepted citation system, consistently used, will be acceptable." Goelz & Watts, Rutter Group Practice Guide: Federal Ninth Circuit Civil Appellate Practice (The Rutter Group 2011), Section 8:211.

There is no rule which mandates a particular citation format but the Harvard Blue Book is the style usually recommended and used. However, if you use any accepted citation system (such as you may find in reported cases), it is fine.