"Who is a Jew?" (Hebrew: מיהו יהודי?‎ pronounced  [/ˈmihu jehuˈdi/]) is a basic question about Jewish identity. The question has gained particular prominence in connection with several high-profile legal cases in Israel since the founding of the Jewish state in 1948.

The definition of who is a Jew varies according to whether it is being considered by Jews for self-identification or by non-Jews for their own particular purposes. As Jewish identity can include characteristics of an ethnicity and of a religion, the definition of who is a Jew has varied, depending on whether a religious, sociological, or ethnic aspect was being considered. This article is concerned with Jewish self-identification issues.

According to the simplest definition used by Jews for self-identification, a person is a Jew by birth, or becomes one through religious conversion. However, there are differences of opinion among the various branches of Judaism in the application of this definition, including:

• Mixed parents: i.e. whether a person of mixed Jewish and non-Jewish parents should be considered Jewish.
• Conversion: i.e. what process of religious conversion should be considered valid.
• Life circumstances issues: i.e. whether a person's actions (such as conversion to a different religion) or circumstances in his or her life (such as being unaware of Jewish parents) should affect his or her Jewish status.

http://en.wikipedia.org/wiki/Who_is_a_Jew%3F