The world-wide sales of polysiloxanes or silicones at the beginning of this new millennium is approximately $10 billion per year. Commercial products range from those entirely composed of silicone to products where the silicone is a low level but key component. This symposium covered the recent academic and technological developments behind silicones and silicone-modified materials and the sessions were well attended of wide interest to both the academic and industrial communities. The papers from our two highly successful symposia in this important area were published in the books Silicones and Silicone-Modified Materials, (Eds. S. J. Clarson, J. J. Fitzgerald, M. J. Owen and S. D. Smith), ACS Symposium Series Vol. 729 / Oxford University Press, 2000, ISBN 0-8412-3613-5 and Synthesis and Properties of Silicones and Silicone-Modified Materials, (Eds. S. J. Clarson, J. J. Fitzgerald, M. J. Owen, S. D. Smith and M. E. Van Dyke), ACS Symposium Series Vol 838 / Oxford University Press, 2003, ISBN 0-8412-3804-9