Klaas te Nijenhuis is a retired Dutch physical chemist and researcher. His achievements include research into the viscoelasticity of thermoreversible polymer networks. He was a Researcher at Delft University of Technology, the Netherlands from 1966 to 1979, then Lecturer from 1979 to 1986 and finally Associate Professor from 1986 until his retirement in 2003. He played a critical role in updating the book for its fourth edition and has kindly offered support and feedback to the new authors for this new fifth edition.