The vibrational behaviour of the azide anion in a variety of environments has been examined by DFT methods. The frequency is sensitive to polar, dipolar and quadrupolar fields. The frequency is also dependent on the metal to which it is bonded and thus to the details of that bonding. Several azides within one molecule can be strongly vibrationally coupled, a coupling which carries with it a transfer of spectral activity. It is suggested that whilst absolute vibrational frequencies carry little immediately accessible information, a combination of infrared and Raman data for the antisymmetric stretch region might give limited structural insights.