Imagined Communities is often cited as the single volume that changed the way that a range of disciplines view nationalism. Written as a response to the failure of Marxist scholars to account for why (typically) men were willing to lay down their life for their country, Anderson equates the nation to a modern religious force in most people's lives, providing them through print and other media technologies with a community that they imagine are carrying out the same activities at the same time in countless locations in the same nation.
I read the whole book (229 pages), from the perspective of critiquing Identity studies, so that I could use this quote:
"Out of this estrangement [from one's own unremembered childhood past] comes a conception of personhood, identity (yes, you and that naked baby are identical) which, because it cannot be 'remembered,' must be narrated. Against biology's demonstration that every single cell in a human body is replaced over seven years, the narratives of autobiography and biography flood print-capitalism's markets year by year." (p.204)
and write this statement:
Anderson (2006) explains in glorious detail how one of the most apparently stable forms of identity - Nationalism - is the product of a particular historical moment, conducive to the economic transformation from imperial state, supported by divine right, to capitalist state, supported by economic might, enabled by mass education, print literacy and linguistic imperialism.
So worth it!!
(This last bit is from my Goodreads.com review)
As a footnote, I found this obituary on the author, but there are plenty of others.