This book has been prepared under the auspices of Commission I.2 on Thermodynamics of the International Union of Pure and Applied Chemistry (IUPAC). The authors of the 18 chapters are all recognized experts in the field. The book gives an up-to-date presentation of equations of state for fluids and fluid mixtures. All principal approaches for developing equations of state are covered. The theoretical basis and practical use of each type of equation is discussed and the strength and weaknesses of each is addressed. Topics addressed include the virial equation of state, cubic equations and generalized van der Waals equations, perturbation theory, integral equations, corresponding stated and mixing rules. Special attention is also devoted to associating fluids, polydisperse fluids, polymer systems, self-assembled systems, ionic fluids and fluids near critical points.