Wagner was an anti-Semite from, at the latest, 1850, when he wrote
'Judaism in Music' (Das Judenthum in der Musik).  The English translation 
of this title is a little misleading, since Wagner has little to say
about Judaism; the article is mainly concerned with the situation of the
Jewish artist (poet or composer) in a non-Jewish culture.  This essay was 
first published anonymously in the 'Neue Zeitschrift für Musik' in two
instalments in September that year. RW took as his starting point earlier
articles in which Theodor Uhlig had attacked Meyerbeer's 'Les Huguenots'.
RW reprinted his article practically unchanged in 1869, thereby provoking
demonstrations at the first performances of 'Die Meistersinger'. It
includes the following assertions (page references are to Wm Ashton Ellis'
English translation of the Prose Works, which follows the 1869 revision):

  1. Jews are hateful (passim)
  2. Judaism is rotten at the core; a religion of hatred (PW3 p90-1)
  3. Jewish composers are comparable to worms feeding on the body of art 
     (PW3 p99)
  4. Jews are hostile to European civilisation (PW3 p84-5)
  5. The Jew rules the world through money (PW3 p81)
  6. The cultured Jew is "the most heartless of all human beings" (PW3 p87) 
  7. The Jews should, like Ahasuerus, "go under" (PW3 p100)
 
RW, however, did not explicitly advocate anything like extermination; in
the afterword to 'Judaism', published with it in 1869, RW explained that
he was arguing for the assimilation of the Jews, which would benefit both
them and their host community. In his private life RW had close Jewish 
friends who appear to have regarded him with considerable affection. 
Nonetheless, his second wife Cosima held strongly anti-Semitic views. 

After RW's death, Bayreuth became a focal point for anti-Semitic and
right-wing individuals, encouraged by Cosima. This culminated in the
marriage of her daughter Eva to the right-wing ideologue, Houston Stewart
Chamberlain, who saw world history in terms of conflict between races. 
The son of Richard and Cosima, Siegfried, was more balanced: "whether a
person is Chinese, a Negro, an American, an Indian or a Jew is to us a
matter of complete indifference".  Siegfried died in 1930, the same year 
as his mother. His English-born widow Winifred had already developed a 
close friendship with Hitler when he was still a young unknown, and she 
was largely responsible for Bayreuth's Nazi links. 

A good starting point for reading about RW's anti-Semitism is the book by
Jacob Katz, 'The Darker Side of Genius'. A number of recent books have
taken a fresh look at this subject, including:

* 'Wagner: Race and Revolution' by Paul Lawrence Rose, who presented a
  view in which racial and anti-Semitic ideas were the driving force behind
  Wagner's creativity, even in 'Der fliegende Holländer'. Many Wagner
  scholars vehemently oppose this view, in particular harshly criticising
  Rose's scholarship; see for example Stewart Spencer's review ('Wagner',
  January 1995, pages 46-48). 

* 'Wagner and the Anti-Semitic Imagination' by Marc Weiner, is a study of
  Wagner's anti-Semitism that has been met with hostility by many
  Wagnerians, although other Wagnerians, including the author of this FAQ
  and also Anthony Arblaster in his review ('Wagner', January 1996, pages
  44-47), think that Weiner sheds light on some dark corners of Wagner's
  character.

These two books refer to earlier articles by Hartmut Zelinsky which
ignited a heated controversy in Germany. Zelinsky interpreted RW as a
proto-Nazi, and attempted to demonstrate that racial and anti-Semitic
schemes lay beneath the surface of RW's music-dramas. Hartmut Zelinsky's
published writings include: 

* In 'Musik-Konzepte 5: Richard Wagner: wie antisemitisch darf ein
  Künstler sein?', ed. H-K. Metger and R. Riehn. Article entitled: 'Die
  Feuerkur des Richard Wagner oder die neue Religion der Erlösung durch
  Vernichtung', Munich 1978. 

* 'Richard Wagner: ein deutsches Thema: Eine Dokumentation zur
  Wirkungsgeschichte Richard Wagners 1876-1976', Frankfurt am Main 1976,
  Vienna 1983. 

* In 'Parsifal: Texte, Materialen, Kommentare', ed. A. Csampai and D.
  Holland. Articles entitled: 'Richard Wagners letzte Karte', 'Der
  verschwiegene Gehalt des Parsifal'. Hamburg 1984.

Although himself a critic of Zelinsky, Barry Millington has presented
arguments for an anti-Semitic theme in 'Die Meistersinger von Nürnberg'.
The relevant articles are: 

* 'Nuremberg Trial: Is There Anti-Semitism in Die Meistersinger?', in
  'Cambridge Opera Journal', volume iii, 1991. Reprinted in 'The Wagner
  Compendium', London 1992. 

* 'Richard Wagner's Anti-Semitism', in the 'Musical Times', December 1996.
  Reprinted in 'Wagner', May 1997, vol. 18 no.2.

Other sources that discuss Wagner's anti-Semitism include 'Aspects of
Wagner' by Bryan Magee (who has also written an interesting article on
the subject, included as an appendix to his 'Wagner and Philosophy');
'Richard Wagner: the Terrible Man and his Truthful Art' by M. Owen Lee;
and Dieter Borchmeyer respectively in chapter 5 of the 'Wagner
Handbook', in an appendix to his 'Richard Wagner: Theory and Theatre'
and in the proceedings of a seminar held in Bayreuth: 'Richard Wagner
und die Juden', ed. D. Borchmeyer, Aami Mayaani and Susanne Vill,
Stuttgart, 2000.

Millington's elaboration of Adorno's suggestion of an anti-Semitic theme
in 'Die Meistersinger' has been discussed (and progressively demolished)
by a number of writers, including: Thomas Grey in 'Deutsche Meister',
ed. Danuser and Münckler; Hans Rudolf Vaget in 'The Opera Quarterly',
no.12, 1995; Dieter Borchmeyer in the Bayreuth 'Festspielbuch' for 1996;
and Hermann Danuser in 'Richard Wagner und die Juden' (see above); most
recently by David B. Dennis in his article, 'Most German of all German
Operas: Die Meistersinger through the Lens of the Third Reich', in
'Wagner's Meistersinger: Performance, History, Representation', ed.
Vaszonyi, pages 98-119.

Hmcw participant Simon Weil has written a study, 'Wagner and the Jews'.  
It can be found online at < http://members.aol.com/wagnerbuch/intro.htm >.