**Preface to "New Frontiers in Anaerobic Digestion (AD) Processes"**

Anaerobic digestion (AD) is widely used to process a variety of organic materials, but a major share of its full potential currently remains unlocked. This Special Issue of the journal *Processes* explores recent developments and advanced concepts related to the valorisation of biomass through the application of anaerobic digestion. Biological phenomena, the efficiency of the AD process, the viability of full-scale AD installations, the integration of hydrogen and biomethane concepts, and biorefineries are some of the themes covered. While AD is addressed under different perspectives, the results all strengthen AD to fulfil its important role as a sustainable and highly versatile technology. Further research and development needs are also presented. The reader is invited to study the publications in detail.

> **Sonia Heaven, Sigrid Kusch-Brandt, and Charles Banks** *Editors*
