[en] The spectrum of three times ionized iridium, Ir IV, was investigated in the 650–2045 Å wavelength region. The analysis has led to the determination of the $5d^6$, $5d^{5}6s$ and $5d^{5}6p$ configurations. Twenty-nine of 34 theoretically possible $5d^6$ levels, 44 of 74 possible $5d^{5}6s$ levels and 150 of 214 possible $5d^{5}6p$ levels have been established. The levels are based on 1348 classified spectral lines. The level structure and transition probabilities were calculated using the orthogonal operators technique. The energy parameters have been determined by the least squares fit to the observed levels. Calculated energy values and LS-compositions obtained from the fitted parameter values are given. The level optimization procedure and the determination of uncertainties of the obtained energy level values are discussed.