[en] Spectroscopic constants and potential energy curves of 30 electronic states of the diatomic ReH are computed using complete active space multiconfiguration self-consistent field followed by first-order configuration interaction (CI) and multireference singles + doubles CI calculations. The second-order CI calculations are made on four low-lying electronic states (T_e < 10,000 cm^-1). The authors also carry out relativistic CI calculations including spin-orbit coupling to compute spin-orbit effects on the low-lying states of ReH. The analysis of the wavefunctions and Mulliken populations reveals that all the low-lying electronic states of ReH are very ionic (Re⁺H^-)