Simone de Beauvoir's "The Second Sex" was one of the most influential books of the twentieth century, and remains the foundation of the feminist movement.
I have read Madame de Beauvoir and the complete uncensoured version of this brilliant piece of work in the original French language. (It's striking that some intellectually challenged reviewers refer to Simone de Beauvoir - one of the most prominent philosophers of the 20 century - as "Simone". In comparison, I can't imagine her lifepartner being addressed as "Jean-Paul", but, of course, referring to prominent women by their first name is a common means of belittling them and their achievements. Read more about it in "The Second Sex".)
Anyone who dismisses the endlessly acute relevance of this masterpiece on human rights as "outdated" - particularly Americans who in 2004 still suffer rampantly archaic sexist issues with women owning the right to their own bodies or the idea of switching the governmental gender balance from a cluster of regressive males to progressive women - only airs their own fundamental ignorance regarding existential conditions for women in a world run by the women-hating male gender.