For decades, our economy has been “linear,” with a “make‐use‐dispose” model ruling every production sector. This model is based in the use of limited feedstock resources as raw materials and generates a large quantity of waste, contributing to a global problem which is causing an irreversible change in the equilibrium of Earth.

To face the problems associated with this linear model, our society demands a change of mind‐set and way of production, with sustainability being the driving force for these changes.

For Chemistry and all of those involved in this area, the answer to these global concerns comes through the application of the 12 principles of Green Chemistry to all chemical sectors; from the small processes carried out in research laboratories to large production of indispensable materials and items used nowadays.

Solvents are widely distributed in many industrial processes, not only in chemistry but they are a paradigmatic example of the unsustainability of the linear production model. The production and use of organic solvents from oil pose challenges in the sustainability field, including the effort and energy required for their disposal as a clean polluting waste. Therefore, scientists are urgently seeking alternatives to these types of media in all research areas.

Deep eutectic solvents (DESs) could be the answer to this, as they fulfill every all requirements of Green Chemistry, making them sustainable solvents which are necessary for a circular economy.

With this book, we intend to offer information on different aspects of these new type of solvents. Each chapter provides a brief description of the context and applicability of the DESs, disclosing both their advantages and disadvantages.

The authors of the different chapters are active researchers in the field, which allows the reader to be introduced easily and quickly into a specific area. Similarly, their experience teaches us about areas that are in their early development or challenges that have not yet been resolved.

The initial chapters introduce the reader to the peculiarities of these types of solvents, with Prof. De Oliveira Vigier and Jérôme describing the synthesis and properties of DESs. Then, Prof. Edler et al. addresses the problem of their possible structure. Finishing this initial set of chapters, Prof. Yang explains the problem of toxicity and biodegradability.

In the second set of chapters, Prof. Verpoorte, Choi et al. describes a special class of DES, the so‐called natural deep eutectic solvents (NADESs), while Prof. Kroon introduces the hydrophobic deep eutectic solvents (HYDESs), as contraposition to typical hydrophilic ones. Finally, Prof. Duarte et al. explains the possible role these especial solvents possess in Nature.

The last set of chapters introduces the use and interactions of DES in different areas. The first discussed area is their use in organic chemistry, with Prof. Capriati et al. describing the use of DESs as possible alternative to organic solvents, Prof. Azizi et al. showing the possibilities of these type of solvents as media and catalysts for several transformations, Prof. García‐Álvarez et al. introducing the use of them as media for metal‐promoted reactions, and finally Prof. Mota‐Morales addressing their use in relevant industrial polymerization processes. The Hayyan's group embarks the reader in a learning experience through the world of the extraction of compounds with biological activity, upnext Prof. Zeng, Lin et al. discusses their application in the valorization of biomass, and Prof. Domínguez de María, Guajardo, and Kara demonstrates the successful use of DESs in biocatalytic processes. In Chapter 14, the preparation and/or functionalization of nanomaterial in DESs is described. In the following chapters, Prof. Ji et al. addresses their possible use as a solution to the environmental problem of CO₂ capture, Prof. Silva shows how DESs can make Analytical Chemistry protocols more sustainable, and finally Prof. Xue, Mu et al. presents the wide range of possibilities that this new type of solvent opens to electrochemical applications.

It is very difficult to predict a general trend for the development of this research area, due to the novelty of the applications of this type of media. However, we could envisage the implementation of these solvents in the near future for industrial purposes, due to the possibility of fine tuning of these solvents to the properties required for particular problems.

As editors, we would like to thank all the contributors, as well as the reviewers, for their participation in this project and for their patience throughout the entire process.

We believe that the use of DESs will change the concept of the necessity of solvents for chemical applications and contribute to the shift from a “linear” to a “circular” way of production, improving our society's DEStiny.