An Energy Services Company, ESE, is a company that generates business by achieving energy savings, and therefore savings in its total costs, to its clients "Customer (economy)").[1]​ ESCOs can improve their energy efficiency and can reduce the environmental impact associated with energy consumption, which is also related to their sustainability and load capacity. The customer saves money without seeing the quality of their products or services diminished.

The European Union is working on defining the minimum requirements to qualify a company as an Energy Services Company. A significant part of the projects developed have to do with the public sector, especially in public buildings, hospitals and outdoor lighting. For example, regarding energy efficiency in public lighting, the European Commission has developed the Greenlight Program, among other initiatives.[2]​.

In Spain, energy services companies are grouped together in the National Association of Energy Services Companies ANESE[3]​ and since 2015 they have awarded the ESEPLUS seal, a seal that accredits those companies and self-employed workers that have the necessary technology, that follow a methodology, that their staff is qualified or that work under the ESE savings guarantee model.[4]​ The first Spanish company that acquired this certificate was the company REMICA") in February of the year. 2015[5]​.

In general terms, Energy Service Companies or Energy Service Companies (ESCO) are companies that are characterized by integrating: i) the technical capabilities of a consulting company, ii) the capital to make investments, and iii) specialized legal support; elements necessary for the successful development of a project.

Once an ESCO identifies a savings or profitable generation potential at the energy user's facilities, it can then carry out the necessary investments, either with its own capital or through financing via financial intermediaries, as long as there are no barriers in the market for the proper functioning of these schemes. The recovery of the investment is obtained with a fraction of the economic savings generated (previously stipulated in the contract); guaranteeing the user savings from the beginning of the project operation.