An electron-spin-resonance study of pure copper phthalocyanine single crystal reveals a highly anisotropic environment. There are strong exchange and dipolar interactions between equivalent sites. However, the exchange interactions between the two nonequivalent sites are small enough to permit detection and separation of the two individual resonances. Values of g and the linewidth have been measured as a function of angle in the three crystallographic planes. The variation of ∆H is discussed in terms of the exchange narrowing, exchange broadening, dipolar broadening, and hyperfine interaction.