Here we briefly review several methods by which infinite dilution activity coefficients can be obtained, and then consider how such data can be used. In particular, we examine the accuracy of predictions of vapor-liquid equilibria over the complete concentration range, and over a range of temperatures based on infinite dilution activity coefficient data at a single temperature. Next, we review the direct use of infinite dilution activity coefficients in estimating the environmental fate of chemicals released into the atmosphere. Finally, the thermodynamics of some systems of biochemical interest are considered.