  This is a commentary on Raoul Bott and Loring Tu's joint article "Equivariant
characteristic classes in the Cartan model," which appeared in "Geometry,
Analysis, and Applications (Varanasi, 2000)," World Scientif Publishing, River
Edge, NJ, 3--20. The article is also included in "Raoul Bott: Collected
Papers," Vol. 5. The commentary discusses the genesis of the article, its
influence, and the current state of the problem concerning equivariant
characteristic classes.
