The growth of distributed renewable resources and the increase of loads due to the electrification of transport and heat sectors will impact on the distribution networks. Besides, the new non programmable and intermittent generators will also reduce the share of traditional rotating and programmable generation, impacting on the stability of the whole system.

However, by providing flexibility, the distributed resources can reduce the need of network reinforcement and support the stability of the system. The procurement of local flexibility should be based on local markets, which have the role of solving local violations and coordinate the provision of flexibility for transmission network services.

The diversity of existing systems and the mutual dependency of flexibility services generates a wide variety of solutions, which are still under experimentation in many countries. The objective of this paper is to review the main projects which have developed flexibility markets, describe their basics characteristics identifying the existing barriers and proposing some possible future evolutions.