The Hall coefficient and resistivity of copper-doped germanium have been measured as a function of temperature over the range 300 °K to 1.8 °K. Typical impurity conduction has been observed. The dependence of the resistivity in the impurity conduction region on the mean separation between the copper impurity centres has been used to estimate the radial extent r₀ of the wave function of the copper ground state. The 0.04 eV copper state is approximately half the size of the 0.01 eV shallow acceptor states. The activation energy in the impurity conduction region agrees well with the theory of Miller and Abrahams. For those crystals containing more than 2 × 10¹⁶ copper atoms/cm³, the resistance in the impurity conduction region decreases in the presence of a magnetic field.