The etching of GaN was investigated in an Ar/Cl-2 inductively coupled plasma. Optical emission spectroscopy and an ion flux probe were used to obtain insight into the etch mechanisms during processing. Langmuir probe measurements were also used to determine the basic Ar/Cl-2 plasma characteristics. Etch rates of approximate to500 nm/min were obtained at relatively low Cl-2 fractions of approximate to50%. The dominant emission species observed were Ga (at 294 nm) and up to six GaCl peaks between 320 and 345 nm. Plasma characterisation and ion flux indicate etch mechanisms that depend strongly on atomic chlorine but with increasing power and at low Cl-2, the significance of ion-based processes cannot be ruled out.