The interaction between the barrier, waste, and surrounding ground may involve thermo-hydro-mechanical and chemical coupled processes that have been analyzed by means of in situ tests, lab experiments, and numerical modeling. Within this context, large scale field tests have been developed to validate research models and gain experience on instrumentation and installation techniques. This book addresses a number of issues concerning engineered clay barriers, including the following topics: field emplacement and instrumentation techniques, fundamental research, material behaviour, and laboratory testing, barrier behaviour and THM modelling, chemical effects, HC, and THMC modeling.