Vibration-rotation lines of C 3 have been identified in the circumstellar spectrum of the obscured carbon star IRC+10216. This molecule is of interest in both the chemistry of flames, where it may be involved in the formation of soot, and in astrophysics, where it is a potential building block for carbonaceous grains. This high-resolution infrared detection of the pure carbon chain molecule C 3 allows the estimation of the equilibrium C-C bond length, 1.297 angstroms. Possible astrophysical formation and destruction mechanisms for C 3 are reviewed, including the relationship between C 3 and carbon clusters.