The central theme of Player Piano is one that resonates even today in 2018, half a century after the book was written; this is the theme of machines versus humans and of science versus humanity. It's a challenge that we face today, with all the discussion around post-humanism and trans-humanism, and it's one that was equally lively in the eighteenth century (consider Rousseau's Discourse on the Arts and Sciences).

Vonnegut depicts a society which exists after a second industrial revolution. In this brave new world, every manual task has been replaced by a mechanical one and most human labor has been replaced with the more efficient machine labor. Everything is measured and those with a sufficiently high IQ get to have elite jobs whereas the rest are left to the Army or professions where they are, as the visiting Shah observes, not that different from the slaves in his country. The revolution has resulted in an immense income inequality. It has also resulted in a complete alienation of humans from their labor: there is an incipient Marxism in the book, at least in this respect. However, Vonnegut is also wary of state authority and depicts in his dystopia a state where everyone is registered, sorted into categories by machines, and closely monitored; there is as little liberty in this state as their is equality.

Player Piano depicts the barrenness—intellectual, emotional, and moral—that follows from a world in which mechanical science and intelligence are given value over all other things, a world in which manual labor is denigrated, and a world which becomes increasingly less human as it becomes scientifically progressive.