Azeotrope refers to a mixture of two or more fluids whose proportions cannot be altered by simple distillation. Azeotropes exhibit the same mass fraction of constituents in the vapor and liquid phases; thus, when boiled, the vapor has the same composition as the liquid. This behavior differs from ideal solutions, where one component is typically more volatile than the others. The azeotrope may have a higher or lower boiling point than the constituents. We study these anomalous fluids because they may exhibit properties that are more advantageous than the constituents. A similar motivation accompanies multi-weight lubricants. In this text we will explore thermodynamic and transport properties as well as applications, including: refrigeration and vapor power cycles.