Yiddish was the language of the Jewish Diaspora - the language of a people on the move across Europe - a mixture of Hebrew and Middle German, spiced with Aramaic, Greek, Latin, Old French and Old Italian.
At its height, it is estimated to have been spoken or understood by more than ten million people.
It has suffered a dramatic decline over the last century.
Many Jews migrated to the USA and adopted English, then there was the Holocaust in which millions of Yiddish speaking Jews were annihilated. The third blow came when Israel decided to adopt Hebrew as its official language.
Dennis Marks travels to New York to discover what has become of Yiddish and how much of the language survives today.
On the Lower East Side, where many Jewish migrants first came to live, he finds a musical and theatrical tradition which once supported a dozen Yiddish theatres on 2nd Avenue.
And he explores the enormous influence of Yiddish culture on American life, its literature and its comedic tradition.
First broadcast on 30th November 2008 on BBC Radio 4.