Very Short Introductions is a series of books (well over a hundred) from the Oxford University Press that offer a brief introduction to some topic. Philosophy, Maths, History, Politics, etc.Each book is abut 10 bucks a pop.They offer boxed sets that give you a discount on a group of books on a similar topic. The Brain Box, for instance, has Evolution, Consciousness, Intelligence, Cosmology and Quantum Theory. The Thought Box has Hegel, Marx, Nietzsche, Schopenhauer and Kierkegaard.My two favorite titles of the boxed sets are The Ballot Box (Politics, etc.) and The Boom Box (Ancient Warfare, Cold War, etc.)