Isobaric quartets in nuclei

The present experimental evidence on $T=\frac{3}{2}$ states in nuclei is presented with particular attention to quartets in which the properties of all four members are known. A relation between the masses of the quartet, the isobaric multiplet mass equation, is shown to hold extremely well. The significance of the coefficients of the equation is discussed, and a brief review of the present status of quintets is also presented.