[en] Electron paramagnetic resonance (EPR) and electron-nuclear double resonance have been used to characterize the neutral copper acceptor in ZnGeP₂ crystals. The copper substitutes for zinc and behaves as a conventional acceptor (i.e. the 3d electrons do not play a dominant role). Because of a high degree of compensation from native donors, the copper acceptors in our samples were initially in the nonparamagnetic singly ionized state (Cu_Zn^-). The paramagnetic neutral state (Cu_Zn⁰) was observed when the crystals were exposed to 632.8 nm or 1064 nm laser light while being held at a temperature below 50 K. The g matrix of the neutral copper acceptor is axial g_par = 2.049 and g_perp = 2.030), with the unique principal direction parallel to the tetragonal c axis of the crystal. The hyperfine and nuclear quadrupole matrices also exhibit c-axis symmetry (A_par = 87.6 MHz, A_perp = 34.8 MHz and P = 0.87 MHz for ⁶³Cu and A_par = 93.9 MHz, A_perp = 37.3 MHz and P = 0.81 MHz for ⁶⁵Cu). Equal hyperfine interactions with the four nearest-neighbour phosphorus ions are well resolved in the c-axis EPR spectrum