The program of the International Conference on Distillation and Absorption, 2002, Baden-Baden included only few lectures on thermodynamics. This article deals with some of the last challenges in thermodynamics related to distillation. Although distillation is considered to be the best understood separation technology, there are still further fields for the thermodynamicists to focus on. It starts with one of the basic steps in designing distillation processes. The acquisition and the handling of property data is shown. The problem of finding the perfect entrainer when extractive distillation is applied to a separation task can be solved with new powerful solvents. This article introduces two comparatively new species of substances. One of the last unresolved areas in distillation was the determination of reaction systems. Latest developments are pointed out. Commonly used models fail to deal with new classes of substances or mixtures which show a complex mixing behaviour. The latest developments in predicting and modelling thermophysical properties focusing on the use of quantum chemistry and powerful equations of state are presented. It will encourage engineers to switch from activity coefficient models to equations of state. (C) 2003 Elsevier B.V. All rights reserved.