Canonical Heinlein, and canonical sci-fi. Was at one time given a great deal of attention for the purported consonance between Martian main character Valentine Michael Smith's worldview and that of the hippies of the 60s, and continues I think to be unfairly regarded as a social commentary, or social satire, or especially a suggestion about how we ought to conduct our affairs here on the real Earth. The extent of its impact though is unquestionable: It made that one Billy Joel song where he was trying to be all R.E.M., and added the word "grok" to the OED.