This book has two aims: to introduce basic concepts of environmental modeling and to facilitate the application of the concepts using modern numerical tools such as MATLAB and FEMLAB. It is targeted at all natural scientists dealing with the environment: process and chemical engineers, physicists, chemists, biologists, biochemists, hydrogeologists, geochemists and ecologists. FEMLAB is a natural complement to MATLAB, as it is a special tool for those tasks which cannot be performed with the basic MATLAB software.