Mesirah (or mesira, Hebrew: to turn over) is the action in which one Jew reports the conduct of another Jew to a non-Rabbinic authority in a manner and under the circumstances forbidden by Rabbinic Law. This may not necessarily apply to reporting legitimate crimes to responsible authority, but does apply to turning over a Jew to an abusive authority, or to a legitimate one who would punish the criminal in ways seen as excessive by Jewish community, though "excessive" punishment by non-Jews may be permissible if a precept of the Torah has been violated.
The term for an individual who commits mesirah is moser or mossur. A person who repeatedly violates this law by informing on his fellow Jews is considered subject to "Din Moser" (law of the informer), which is analogous to "Din rodef" in that both prescribe death for the offender, and according to some, in some circumstances he may be killed without warning. 
According to The Times of Israel and a Channel 4 investigation, the concept of mesirah was used by a Haredi leader to protect community members investigated for child molestation from police investigation.
The principle of mesirah has also been used to dissuade Jewish auditors from reporting other Jews to the IRS for tax fraud.
Rabbinic courts in Israel have been known to issue writs calling for social exclusion of Jews bringing legal issues to Israel's civil courts.
The mesirah doctrine came under intense public scrutiny in Australia in early 2015 as a result of evidence given to the Royal Commission into Institutional Responses to Child Sexual Abuse relating to an alleged long-running and systematic cover-up of child sexual abuse and the institutional protection of perpetrators at the exclusive Melbourne boys' school Yeshiva College. Fairfax Media on 28 January 2015 reported secret tape recordings and emails had been disclosed which revealed members of Australia's Orthodox Jewish community who assisted police investigations into alleged child sexual abuse were pressured to remain silent on the matter. Criminal barrister Alex Lewenberg was alleged to have been "disappointed", and to have berated a Jew who had been a victim of a Jewish sex offender and whom he subsequently regarded as a mossur for breaking with Mesirah tradition.
In February 2015 Mr Zephaniah Waks, an adherent of the ultra-Orthodox Hasidic Chabad sect in Melbourne, Australia, testified to Royal Commission that following his discovery that one of his sons had been sexually abused by Rabbi David Kramer, a teacher at their school, Yeshiva College, he confronted the school's principal, Rabbi Abraham Glick and demanded that Kramer be sacked. Mr Waks told of his shock when he learned a few days later that Kramer was still working at the school, and that he again confronted Rabbi Glick, who then claimed that Kramer had admitted his guilt "because he wanted to be caught" but that the school could not dismiss Kramer because (Glick claimed) he was at risk of self-harm. Mr Waks also told the Commission that despite his anger, he felt constrained not to go to the authorities because of the doctrine of mesirah:
- " I thought this was absolutely outrageous, however if I reported this to the police I would be in breach of the Jewish principle of mesirah.”
- Waks said the concept of “mesirah” prevented members of the ultra-Orthodox Chabad sect of Judaism from going to non-secular authorities.
- “At the very least, the breach of mesirah almost certainly always leads to shunning and intimidation within the Jewish community and would almost certainly damage marriage prospects of your children.”
Giving evidence to the Commission on the day before his father, Mr Menachem (Manny) Waks, one of three children from the Waks family who were sexually abused by staff at Yeshiva College, testified that after breaking mesirah by going public about his abuse, he and his family had been ostracised by rabbinical leaders, shunned by his community and subjected to a sustained campaign of abuse, intimidation and threats, which eventually forced Mr Waks to leave Australia with his wife and children. He also testified about how members of the exclusive Chabad community had pressured him to abandon his advocacy:
- "I was in fact contacted by several considered community members, and they said to me that the anti-Semites are having a field day with my testimony and my publicity around this issue, and that if I cared about the community, I'd cease doing that straight away."
Counsel Assisting the commission then asked Mr Waks how he felt having been accused of being an informer:
- "I am appalled by it obviously, because the concept of 'Mesirah' really, you can become a death target. Taken at its literal meaning, you become potentially a target who is legitimate to be murdered, because you've gone and cooperated with the authorities. Now, I've never felt threatened for my life, but it does highlight the severity in which this concept is held."
- "Informing on Others for Violating American Law: A Jewish Law View". jlaw.com. Retrieved 4/9/2014. Check date values in:
- "Mesirah: Two Contemporary Views". torahmusings.com. Retrieved 4/9/2014. Check date values in:
- Sex-Abuse Cover Ups: The Mesirah Mess Tuesday, June 5, 2012, The Jewish Week
- Rabbi Michael J. Broyde. "Informing on Others for Violating American Law: A Jewish Law View". Retrieved 2012-08-19.
- Alfred S. Cohen (1984). Halacha and contemporary society. KTAV Publishing House, Inc. pp. 100–. ISBN 978-0-88125-042-8. Retrieved 27 February 2011.
- Informing on Others for Violating American Law: A Jewish Law View. "Broyde".
- Miriam Shaviv. "UK Haredi chief caught telling alleged victim not to tell police about abuse". The Times of Israel.
- "Parents ignore child abuse at rabbi's advice". Ynet News.
- Joshua Hammerman. "Sex-Abuse Cover Ups: The Mesirah Mess". The Jewish Week.
- "'Many ultra-Orthodox rabbis view use of state courts, in Israel and in the Diaspora, as a violation of a principle of Jewish law.' (May 22, 2013) The Jerusalem Post" http://www.jpost.com/National-News/Court-to-review-rabbinical-courts-social-exclusion-order-313935
- Melissa Davey, "Rabbi was allowed to keep teaching after admitting abuse of children, inquiry told", The Guardian, 3 Feb. 2015
- Samantha Donovan, "Royal Commission hears Jewish school failed to deal with serial child abuser", PM", ABC Radio National, 2 Feb. 2015