Laser selective excitation, excited state absorption, two-photon absorption, and fluorescence line narrowing techniques have been used to investigate the electronic energy level structure of the Cm3+ ion diluted in the host crystal Cs2NaYCl6. In this crystal the Cm3+ ion replaces a Y3+ ion at an octahedral site (O-h symmetry). Analysis of these spectra resulted in the assignment of 52 energy levels, which were fitted to the parameters of an empirical Hamiltonian with a rms deviation of 57 cm(-1). Many of the Gamma(8) symmetry levels exhibited small splittings, which was indicative of a site symmetry lower than O-h. The energies of the most prominent vibronic features have been measured and assigned to specific vibrational modes of the CmCl63- moiety or to lattice modes. The lifetimes of four fluorescing levels have been obtained at room and liquid helium temperatures. These were analyzed to determine the processes which contribute to the relaxation of an excited Cm3+ ion in this host. Blue P-6(5/2)-->S-7/2 upconversion fluorescence was observed when pumping the orange S-8(7/2)-->D-6(7/2) absorption transitions and explained by a phonon-assisted energy transfer mechanism.