In order to convert, the conversion candidate must have a circumcision (males) and immerse in the mikveh before a kosher beth din, comprising three Jewish males who are shomer Shabbat.[1] There is also a requirement to accept the commandments (although not necessarily a commitment to keep the mitzvot), although without this step there are many authorities who will accept the conversion as valid. In the past it is likely that conversions happened like this, and were decentralized, and universally accepted once performed.