The increase of renewables in the electricity mix in Europe in the last years and the plans to shut down coal-fired power plants will change the power system operation rules. Expectations are that small unit aggregators can soon provide flexibility and balancing services in several European countries. This paper aims to perform a qualitative comparison of European market rules for small-scale-scale flexibility. The work focused more specifically on the prequalification process that the Balancing Service Providers should develop to participate in Frequency Containment Reserve Services and the specific needs of the small-scale flexibility and balancing providers. Five countries were chosen for the analysis: Switzerland, Belgium, Germany, Portugal, and Spain. Of the five countries compared, the one that appears to have fewer entry barriers and shows greater possibilities of working on a case-to-case basis is Switzerland, followed by Belgium and Germany. Portugal and Spain are developing their ancillary service markets and should soon allow the participation of small-scale balancing providers in ancillary services.