Murray Gell-Mann shows that the strongly interacting particles—baryons and mesons—display an approximate unitary symmetry described by the group SU(3) and form families of multiplets (singlets, octets, and decuplets). The framework developed here leads to the quark model, and is a crucial step in the development of the standard model of elementary particle physics. Gell-Mann is awarded the 1969 Nobel Prize in Physics for this work.