We were delighted to host the sixth International Conference on Aperiodic Crystals APERIODIC'09 in Liverpool in September 2009, and thank all participants for their contributions and their support.

The proceedings have now been published electronically as volume 226 of Journal of Physics: Conference Series. All papers in the proceedings volume are open access. Printed copies of the proceedings volume will be mailed to participants soon.

Aperiodic'09 was the sixth International Conference on Aperiodic Crystals, organized under the auspices of the Commission on Aperiodic Crystals of the International Union of Crystallography (IUCr). It followed Aperiodic'94 (Les Diablerets), Aperiodic'97 (Alpe d'Huez), Aperiodic'2000 (Nijmegen), Aperiodic'03 (Belo Horizonte) and Aperiodic'06 (Zao). The next conference in this series will be held in Australia in 2012, organised by Ray Withers.