QZ Carinae is an O-type, double-lined, eclipsing binary in the Carina Nebula. A radial-velocity study shows that this system actually consists of two single-lined spectroscopic binaries in the same line of sight, probably in wide orbit about each other. In one of these binaries, which undergoes eclipses with period 5.9980 days, the primary has spectral type roughly O9 III and produces the weaker of the two observed sets of spectral lines. The star responsible for the stronger set is 0.6 mag brighter, has spectral type O9.5 I, and moves in an eccentric orbit about an unseen companion with period 20.73 days. Radial velocities are presented and orbits are determined for both systems. A systematic difference in velocity between He I and Si IV in the supergiant suggests appreciable mass loss. Spectrograms show broad H-alpha emission, which appears to vary in phase with the eclipsing binary.