The far infra-red bimolecular collision induced absorption of compressed gaseous cyanogen has been studied in the region 20–120 cm–1, at pressures of up to 33.5 bar, together with the liquid spectrum at 301 K in the same region. From the integrated intensity of the gaseous absorption an apparent quadrupole moment of ±(14.7 ± 2.0)× 10–26 e.s.u. was computed. A MO calculated value of –9.0 × 10–26 e.s.u. has been quoted (McLean). For the liquid an apparent molecular quadrupole moment of ±(6.9 ± 1.0)× 10–26 e.s.u. was deduced, the much lower value reflecting inter alia the reduced efficacy of multi-molecular collisions in generating induced dipoles.