Ohio Revised Code Title XXIX. Crimes Procedure § 2945.42

No person is disqualified as a witness in a criminal prosecution by reason of the person's interest in the prosecution as a party or otherwise or by reason of the person's conviction of crime.  Husband and wife are competent witnesses to testify in behalf of each other in all criminal prosecutions and to testify against each other in all actions, prosecutions, and proceedings for personal injury of either by the other, bigamy, or failure to provide for, neglect of, or cruelty to their children under eighteen years of age or their child with a mental or physical disability under twenty-one years of age.  A spouse may testify against his or her spouse in a prosecution under a provision of sections 2903.11 to 2903.13, 2919.21, 2919.22, or 2919.25 of the Revised Code for cruelty to, neglect of, or abandonment of such spouse, in a prosecution against his or her spouse under section 2903.211 or 2911.211 of the Revised Code for the commission of the offense against the spouse who is testifying, in a prosecution under section 2919.27 of the Revised Code involving a protection order issued or consent agreement approved pursuant to section 2919.26 or 3113.31 of the Revised Code for the commission of the offense against the spouse who is testifying, or in a prosecution under section 2907.02 of the Revised Code for the commission of rape, under section 2907.03 of the Revised Code for the commission of sexual battery, under section 2907.04 of the Revised Code for the commission of unlawful sexual conduct with a minor, under section 2907.05 of the Revised Code for the commission of gross sexual imposition, under section 2907.06 of the Revised Code for the commission of sexual imposition, under division (B)(2) of section 2907.07 of the Revised Code for the commission of importuning, or under former section 2907.12 of the Revised Code for felonious sexual penetration against such spouse in a case in which the offense can be committed against a spouse.  Such interest, conviction, or relationship may be shown for the purpose of affecting the credibility of the witness.  Husband or wife shall not testify concerning a communication made by one to the other, or act done by either in the presence of the other, during coverture, unless the communication was made or act done in the known presence or hearing of a third person competent to be a witness, or in case of personal injury by either the husband or wife to the other, or rape or the former offense of felonious sexual penetration in a case in which the offense can be committed against a spouse, or sexual battery, unlawful sexual conduct with a minor, gross sexual imposition, sexual imposition, importuning, public indecency, or bigamy, or failure to provide for, or neglect or cruelty of either to their children under eighteen years of age or their child with a mental or physical disability under twenty-one years of age, violation of a protection order or consent agreement, or neglect or abandonment of a spouse under a provision of those sections.  The presence or whereabouts of the husband or wife is not an act under this section.  The rule is the same if the marital relation has ceased to exist.