Partial molar properties are useful thermodynamic properties because their molar average equals the property itself. In this article, we present a description of partial properties in general, and we show that for many partial properties, partial molar properties being a subset, the property is a molar average of the partial properties. Although partial molar properties remain the most useful, several of the other partial properties could have practical applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009