There are six quarks, but physicists usually talk about the three pairs of quarks: Up/Down, Charm/Strange, and Top/Bottom. For each of these quarks there is a corresponding antimatter-quark (anti-quark.)

Quarks have the unusual characteristic of having fractional electric charge of either 2/3 or -1/3, unlike the -1 charge of an electron and the +1 charge of the proton. Quarks also carry another type of charge called color charge, which has to do with strong forces, found later in this section.