This book gives the reader a brief introduction to the COMSOL Multiphysics software tool. Building COMSOL Multiphysics models in 2D or 3D will help students to consolidate their skills by applying basic theory to the real modelling of tasks that in the recent past would require months of programming and dedicated projects to solve a single problem. The examples illustrated in this book include modelling of heat transfer, the migration of a radioactive species in a channel using the Navier-Stokes equations and a chemical heterogenous reactor. These are problems that tend to be rather abstract until such time as a student applies these fundamental equations in practice. Advanced coupling between phenomena in fields such as electromagnetics with others such as heat transfer and computational fluid flow is made easy in COMSOL Multiphysics. A short introduction to the basics, concepts and techniques will allow the reader to progress rapidly and start developing his/her own models. In the second part of this book, some of the models developed in the first part are used to create model applications that can even run on a mobile phone. About the authors: António de Campos Pereira, PhD. in Physics, is an author and consultant. He is a retired researcher from the Dept. of Physics at Stockholm University. Prof. Isabel Paiva, Ph.D. in Chemical Engeneering, is a researcher at C2TN at IST, the School of Engineering of the University of Lisbon. Marcus Inácio has a B.Sc. in Electrotechnical Engineering and is specialising in the field of Medical Physics at KTH, the Royal Institute of Technology in Stockholm, Sweden. Hugo de Campos Pereira is an environmental engineer from Uppsala University and a Ph.D. student specialising in the sorption of highly fluorinated compounds in soils at the Department of Soil and Environment at SLU, the Swedish University of Agricultural Sciences in Uppsala, Sweden.