One way to understand the world is by looking at its most basic building blocks. All the substances in the world are made up of atoms, which interact with each other by exchanging or sharing electrons. Deep within the atom lies the nucleus, which itself contains the elementary particles called quarks. And by building powerful particle accelerators and enormous detectors, physicists are able to probe the most fundamental constituents of matter. The Nature of Matter is a compelling guide that identifies the essential qualities and characteristics by which matter is recognized.