The beta and alpha phases of CuAlCl4 have been characterized by solid-state Al-27 and Cu-63 magic angle spinning nuclear magnetic resonance. The very short spin-lattice relaxation times of the copper spins, and the sensitivity of the I = (3)/(2) Cu-63 nucleus to the small differences in the local structure of Cu in the two phases, allowed Cu-63 spectra to be acquired in very short time periods (1 min), in which the beta and alpha phases were clearly resolved. This time resolution was exploited to follow the phase transition from the pseudohexagonal close-packed beta -CuAlCl4 into the pseudocubic close-packed alpha -CuAlCl4, which occurs above 100 degreesC. In situ time-resolved Cu-63 MAS NMR and synchrotron X-ray diffraction experiments were used to measure the kinetics of this phase transition as a function of temperature. The transformation was shown to be a first-order phase transition involving no intermediate phases with an activation energy of 138 kJ/mol. The kinetic data obey a first-order Avrami-Erofe'ev rate law. A one-dimensional growth mechanism is proposed that involves a combination of Cu+ ion self-diffusion and a translational reorganization of the close-packed anion layers imposed by the periodic rotations of [AlCl4](-) tetrahedra. This beta to alpha phase transformation can be induced at ambient temperatures by low partial pressures of ethylene.