This book—published under the auspices of IUPAC and its affiliated body, the International Association of Chemical Thermodynamics (IACT)—serves as a guide to scientists or technicians who use equations of state for fluids. Concentrating on the application of theory, the book contains a discussion of the practical use of each type of equation and addresses the strengths and weaknesses of each one. It includes material on the equations of state for chemically reacting and non-equilibrium fluids that have undergone significant developments. The books also updates the equations of state for fluids and fluid mixtures. To address the needs of practitioners within academia, government, and industry, an international team of distinguished experts was assembled to provide each chapter. The topics covered in the book are important to the energy business, especially the hydrocarbon economy and the development of new power sources, which are also significant in the application of liquid crystals and ionic liquids to commercial products. Post-graduate researchers in the fields of chemical engineering, mechanical engineering, chemistry, and physics will find this book to be a useful reference.