Any natural or legal persons (e.g. any company, big or small, research organisations, universities, non-governmental organisations, etc.) regardless of their place of establishment or residence. They must possess the operational and financial viability to carry out the research tasks that they propose.
To see exactly whether you are eligible for funding, check the specific work programme or call for proposal/tender.
Most of the H2020 themes support collaborative research projects where at least three organisations from different countries form a consortium. However, there are a number of opportunities also for mono-participant actions: