I recently learned of a relationship between the representations of the groups $SO(p,q)$ and $SL(2,\mathbb{R})$ which is part of an apparently much larger set of ideas known as Howe Duality. My question is a bit open ended, but can someone point me to a good entry point (review articles, lectures) for learning more about Howe duality and in particular the $SO(p,q)$-$SL(2,\mathbb{R})$ duality? Thanks.



SO(p,q) and Howe Duality
A good introduction is "Non-Abelian Harmonic Analysis: Applications of SL(2,R)" 
by Roger Howe and Eng Chye Tan, especially Chapter III, Section 2.


