CML (Centrum voor Milieuwetenschappen Leiden), the Institute of Environmental Sciences, Leiden University, was founded as an interfaculty university institute in 1977. Helias A. Udo de Haes has been its founding father and director from the beginning. The debate on LCA 'entered' with the CML environmental sciences (see the Appendix, 'The CML Story: How Environmental Sciences Entered the Debate on LCA', pp. 127–132). This Special Issue of Int J LCA is honouring Helias Udo de Haes who will retire from his Chair at Leiden University this summer. For this honouring issue, contributions from a selected number of colleagues and friends of Helias have been invited. Their articles reflect the developments that have been and are still taking place within the dynamic world of Life Cycle Assessment. It highlights the enormous progress that has been made in the scientific underpinning of LCA and the important contribution of Helias to a developable framework of LCA. - - - Cover design: Edwin Grondinger, abavo GmbH, Nebelhornstraße 8, 86807 Buchloe, Germany (edwin.grondinger@abavo.de; http://www.abavo.de)
