**4. Conclusions**

This paper has analyzed the main trends in global research on intelligent contracts, highlighting the main countries that have made a scientific effort in this area, in order of importance—the USA, China, the United Kingdom, Germany, and Italy—and scientific collaboration between these countries does not necessarily respond to obvious or expected trade relations. For example, in the case of Spain, the relationship is concentrated mainly with Canada, Iran and the United Kingdom. The publication of research, mainly in the form of communications in congresses, shows that intelligent contracts are emerging technologies and still in the initial study phase, unlike other more established technologies that do the same work in the form of articles or even books. In order of importance, the main subject areas found were computer science, engineering, mathematics, energy, social sciences, business, management, and accounting. In the absence of a greater degree of maturity and widespread use, smart contracts raise several legal issues that need to be addressed. Consequently, this paper demonstrates that the Social and Legal Sciences occupy the fifth position in the number of published papers, clearly indicating that the technological aspect of this issue needs to be given a legal character, as its implications and scope are of the utmost interest for the international scientific community. Therefore, further legal progress must be made on the reality of this new form of contracts, especially to support the two main lines towards which they have evolved—electronic money and energy costs.

Finally, the analysis of the themes of all these works, by means of the analysis of the keywords, have shown that there are 6 clearly differentiated clusters around which all these works can be grouped. Their temporal evolution shows a tendency towards two main lines of research—the electronic money (cryptocurrencies, or bitcoins) and the smart power grids and electricity market (electricity consumption, electric industry). Given the growing scientific interest shown by the growing number of publications, smart contracts can overcome the problems pointed out by many detractors, and they could be a driver of sustainability. For environmental sustainability applications, smart contracts should pay particular attention to small communities, since it has been observed that small communities are still poorly covered by this particular technology, in spite of often being stewards of natural resources.

**Author Contributions:** E.S.-M. and F.M.-A. have contributed in the same way to the writing of this manuscript, both authors have read and approved the final manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors of this manuscript wish to thank the CIAIMBITAL research center for its support of this research.

**Conflicts of Interest:** The authors declare no conflict of interest.
