Dr. Pierre Cornelis Thijssen studied chemistry at the Radboud University Nijmegen in the Netherlands, obtaining his Master’s Degree in 1978. He then moved to the University of Amsterdam in the Netherlands, where he graduated in 1986 with a PhD based on his thesis entitled “State Estimation in Chemometrics,” which is the basis of this book. Since then, Dr. Thijssen has worked for various companies as a laboratory manager and chemometrician. Dr. Sillas Hadjiloucas received his Master’s Degree in Pure & Applied Biology in 1992 from the University of Leeds, United Kingdom, and in 1996, a PhD in Cybernetics from the University of Reading, United Kingdom. He worked on his Postdoc in Germany until the end of 1999. Dr. Hadjiloucas had worked as permanent member of Staff at Reading since January 2000, originally at the School of Systems Engineering (Cybernetics) and later transferred to the newly formed Bio-Engineering Department at Reading in Autumn 2016. His current appointment as Associate Professor is a joint one combining teaching and research.