The 31st Leeds-Lyon Symposium on Tribology was held at Trinity and All Saints College in Leeds under the title "Life Cycle Tribology" from Tuesday 7th September until Friday 10th September 2004. Over the three days of presentations that followed, life cycle tribology was explored across a range of areas including automotive tribology, bearings, bio-degradability and sustainability, bio-tribology, coatings, condition monitoring, contact mechanics, debris effects, elastohydrodynamic lubrication, lubricants, machine systems, nanotribology, rolling contact fatigue, transmissions, tribochemistry and wear and failure. Invited talks in these fields were presented by leading international researchers and practitioners, namely C.J. Hooke, J.A. Williams, R.J.K. Wood, G. Isaac, S.C. Tung, D. Price, I. Sherrington, M. Hadfield, K. Kato, R.I. Taylor, H.P. Evans, R.S. Dwyer-Joyce and H. Rahnejat.