It has long been acknowledged that the Ballantine Adult Fantasy program changed the very shape of the field, doing almost as much as Tolkien to make fantasy novels into the huge part of the market they are today.
http://en.wikipedia.org/wiki/Ballantine_Adult_Fantasy_series
When I came across this ad in the February 1969 issue of GALAXY magazine, I thought it to be a seminal document not often--if ever--reprinted.
