**Preface to "Finite-Time Thermodynamics"**

Finite-time thermodynamics, as a field of theory as well as an application, was initiated 45 years ago. As is often the case when new concepts crystalize, stray ideas about "what if" had appeared earlier (e.g., Chambadal in 1957, Novikov in 1958, Curzon and Ahlborn in 1975, and Weinhold in 1975), but it was only in 1976 that a more comprehensive net of theory started to evolve. At the same time, it became clear that the restriction of finite time, or in general finite resources, is pervasive for all real processes. The "finite-time" idea spread to chemistry, physics, economics, engineering (under a different name and with preciously few references to its origin), and, in more recent years, to biology. It is now a solidly established field with an exceptionally wide range of applications.

In the present Special Issue of *Entropy*, we have collected 19 papers which provide a wide range of current topics for which finite time is a crucial element, some very abstract, some very applied, and some in unexpected directions. To wrap up the package, one paper provides a personal view of the beginnings, and one paper is our look into the crystal ball for the future. A lot more FTT and FTT-inspired research is on its way. Happy reading.

> **R. Stephen Berry, Peter Salamon, and Bjarne Andresen** *Editors*
