The privilege of not being compelled to testify against one’s husband or wife has ancient roots.  Writing in 1628, Lord Coke observed that “It hath been resolved by the justices that a wife cannot be produced either against or for her husband.”   1 Coke A Commentary upon Littleton 6 b (1628).  As cited by the Supreme Court in Trammel v. United States (1984) 445 U.S. 40. In California it is well-settled that a married person has a privilege not to testify against such person’s spouse in a civil or criminal action, irrespective of whether or not the spouse  is a party to the action.  Jefferson, Evidence Bench book 2nd Edition at p. 1337. At the outset, it must be established that as a general rule before a spouse may  testify against her husband in a criminal proceeding her prior express consent must be obtained. Evidence Code §971. 
  Evidence Code §972 delineates certain exceptions to the general rule cited above exclaims one Criminal Attorney in Torrance .  The prosecution in any given criminal case can assert that an exception exists to the marital privilege   For example,  Evidence Code §972(e)(1) which states: a married person does not have a privilege in a criminal proceeding in which one spouse is charged with a crime against the person or property of the other spouse or of a child. However, in order for this exception to apply the prosecution has the burden of proof to establish those preliminary facts by a preponderance of the evidence.
                The California criminal case of Fortes v. Municipal Court (1980) 113 Cal. App. 3d 704 is instructive. In Fortes, the Appellate Court held that under Evidence Code §405, the prosecutor as the party claiming the  applicability of the exception to the marital privilege set forth in Evidence Code §972(e)(2), had the burden of proving the preliminary facts to make the exception to the privilege applicable.  The Fortes Court interpreted Evidence Code §972(e)(2) as meaning that a mere charge that a defendant  was engaged in committing an offense against his spouse is insufficient proof in bringing the exception into play.