The Nazi policy of exterminating European Jews and other races deemed 'inappropriate'. Introduced by Heinrich Himmler and administered by Adolf Eichmann, the policy resulted in the murder of 6 million Jews and millions of others in concentration camps between 1941 and 1945.

That if the genocide of the Jews was an official policy of the Nazi government then a document signed by Adolf Hitler ordering their annihilation would have been found by now. There is a document signed by Hitler authorising the euthanasia program. How come there is no Hitler-signed order authorising the 'Final Solution'?
David Irving has "offered a thousand pounds to any person who could produce even one wartime document showing explicitly what Hitler knew, for example, of Auschwitz . On his web site Irving states that "nobody has yet claimed the widely publicised $1,000 reward . . . for even one page of wartime contemporary evidence that Hitler was even aware of Auschwitz ('the Holocaust'), let alone gave the order for the Final Solution."
John Weir, writing on CODOH [Committee for Open Debate on the Holocaust], a prominent American Holocaust denial web site, argues that if such an order was issued "it would have been located... Since none has been found, the conclusion is inescapable.

It is very unlikely that Hitler ever signed such an order for the following reasons:
Hitler and the Nazi regime were very secretive about the 'Final Solution.' Hitler didn't want to leave an evidence trail that would inflame his own population or the leadership of other countries.
Heinrich Himmler, the head of the SS, in a speech given at Poznan (Posen, Poland) to a meeting of Major Generals on October 4, 1943, acknowledged how secret the Final Solution was: "We will never speak of it publicly. . . I mean the evacuation of the Jews, the extermination of the Jewish race. ... The Jewish race is being exterminated... that's quite clear, it's in our program elimination of the Jews and we're doing it, exterminating them . . . This is a page of glory in our history which has never been written and is never to be written . . ."