The economy dematerialization is a means to promote sustainable development as it eliminates or reduces the use of natural resources, being the intensification of technological processes a way to dematerialize the economy. More compact and efficient systems require fewer resources. In what concerns technological systems involving heat exchange processes, intensification results in the reduction of the exchanging area, the amount of working fluid or both, which, in addition to other advantages inherent to systems' miniaturization, is a direct contribution of the scientific and technological development to a more sustainable society. The development of nanofluids is a response to such challenges of contemporary society, contributing to the innovation of products and systems by solving fundamental questions raised at the level of basic sciences. This book presents the methodologies to correctly prepare long-term nanofluids as well as a solid database and a general physical-mathematical model to determine their thermal conductivity.