One of the most interesting theories, in my opinion, is that of Shulamith Volkov. She argues that, rather than any theological consideration, antisemitism acted as shibboleth for conservatives to express their opposition to modernism. So, they weren't interested in attacking kosher practices or the word of the Torah, that is, Judaism; they were instead opposed to industrial capitalism, socialism, cosmopolitanism, in favour of a strong nation etc, and in the Jews they had a transnational ethnic grouping onto which to project those qualities. Rather than say 'I oppose these things, and support these other things', one could simply say 'I am an antisemite' and that was that. It's a very good article, and it goes a good way toward explaining the type of antisemitism that sprang up in the nineteenth century and lingered into the twentieth, but it's not the full story.

For a good but brief overview of the different types of antisemitism, it's worth taking a look at Samuel Salzborn's paper, which covers what he believes are the main types. These are: traditional religious antisemitism (ie. anti-Judaism), nationalist antisemitism (more or the less the type Volkov discusses), seconday antisemitism (such as holocaust denial), antizionist antisemitism (ie. anti Israeli state), and a look at Arab/Muslim antisemitism, which is another kettle of fish altogether.

You can download the Salzborn here: (http://ieg-ego.eu/en/threads/transnational-movements-and-organisations/international-social-movements/samuel-salzborn-antisemitism/at_download/dnb)

Shulamith Volkov, 'Antisemitism as a Cultural Code. Reflections on the History and historiography of Antisemitism in Imperial Germany' in Yearbook of the Leo Baeck Institute xxiii (1978) pp 25-45.