The Judaizers were a faction of the Jewish Christians, both of Jewish and non-Jewish origins, who regarded the Levitical laws of the Old Testament as still binding on all Christians. They tried to enforce Jewish circumcision upon the Gentile converts to early Christianity and were strenuously opposed and criticized for their behavior by the Apostle Paul, who employed many of his epistles to refute their doctrinal positions.

The term is derived from the Koine Greek word Ἰουδαΐζειν (Ioudaizein), used once in the Greek New Testament (Galatians 2:14), when Paul the Apostle publicly challenged the Apostle Peter for compelling Gentile converts to early Christianity to "judaize". This episode is known as the incident at Antioch.

Most Christians believe that much of the Old Covenant has been superseded, and many believe it has been completely abrogated and replaced by the Law of Christ. The Christian debate over Judaizing began in the lifetime of the apostles, notably at the Council of Jerusalem and the incident at Antioch. It has been carried on parallel to continuing debates about Paul the Apostle and Judaism, Protestant views of the Ten Commandments, and Christian ethics.