The short answer
Traditionally, a qualified beit din. Because Jewish authority is decentralized, the answer also depends on which community's standards you are asking about — there is no single universal arbiter.
Why people ask this
People often assume there is a 'head of Judaism' who can certify a conversion. Understanding that authority is dispersed explains both the freedom and the frustration.
Key terms
- Posek /po-SEK/
- A decisor of Jewish law.
Jewish perspectives
- Orthodox: a recognized beit din of qualified rabbis; acceptance can vary by community.
- Conservative/Masorti: the movement's law committee and its rabbis.
- Reform: the rabbi and community under Reform principles.
Scholarly & historical context
Since the end of centralized institutions like the Sanhedrin, halachic authority has rested with qualified local and regional courts and posekim, producing real, recognized diversity.
What is agreed upon
A qualified beit din administers and validates a conversion for its community.
Where the disagreement begins
Which batei din and which kabbalat mitzvot standards qualify, and whether one community must defer to another's.
Practical consequences
Ask the community you hope to join which beit din it accepts, and convert under that authority.
Original sources
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