The structural, elastic and vibrational properties of the ternary semiconductor chalcopyrite are studied using the pseudopotential method within the local density approximation. The lattice constants and internal parameter are in good agreement with experiments. The elastic moduli derived from the stresses generated by small strains compare favourably with experiments and the material is elastically anisotropic. All zone-centre phonons are determined by diagonalization of the dynamical matrix derived from the forces generated by small ionic displacements. The calculated phonon frequencies are in excellent agreement with experiment and can be grouped into three bands. Two silent modes are also obtained. The eigenvectors are used to discuss the three-band phonon spectrum and the spectroscopic activity of the modes.