The present paper presents a systematic investigation of both catalyst free and catalyst assisted AlN nanowire synthesis by chemical vapour deposition using Al and NH3 as source materials. Growth runs have mostly been carried out at 1100 degrees C under H-2 as carrier gas. While the catalyst free growth runs resulted in long (similar to 40 mu m) and dense AlN nanowire array films, the catalyst assisted growth resulted in short nanowires (3-5 mu m). Growth mechanisms have been presented. Raman spectroscopy of the catalyst free grown nanowires has revealed very symmetric and strong phonon modes [e.g. strong E-2 (high)] indicating very good crystal quality of the grown AlN nanowires. In brief, catalyst free growth eliminates catalyst contamination and produces high quality and density of long nanowires, which is very valuable for scale-up manufacturing opportunities of the AlN nanostructures.