ESO, the European Organisation for Astronomical Research in the Southern Hemisphere, is an inter-governmental organisation with 15 Member States*. These member states are:

	Country	Formally joined	Member number	Scale of contribution % (2013)	Contribution (kEUR, 2013)	More info	ESON mini-site	Local Time
	Austria	2009	14	2.53	3,353	ESO & Austria	Austria	check local time
	Belgium	1967	Founding member	3.20	4,241	ESO & Belgium	Belgium	check local time
	Brazil	Ratification pending	15	—	—		Brazil	check local time
	Czech Republic	2007	13	1.05	1,392		Czech Republic	check local time
	Denmark	1967	6	2.04	2,704		Denmark	check local time
	Finland	2004	11	1.55	2,054		Finland	check local time
	France	1964	Founding member	16.39	21,721	ESO & France	France	check localtime
	Germany	1964	Founding member	22.78	30,190	ESO & Germany	Germany	check local time
	Italy	1982	8	11.68	15,479		Italy	check local time
	Netherlands	1964	Founding member	5.27	6,984		Netherlands	check local time
	Portugal	2001	9	1.17	1,551	ESO & Portugal	Portugal	check local time
	Spain	2007	12	7.99	10,589	ESO & Spain	Spain	check local time
	Sweden	1964	Founding member	3.55	4,705		Sweden	check local time
	Switzerland	1982	7	4.52	5,990		Switzerland	check local time
	United Kingdom	2002	10	16.28	21,574		UK	check local time

* Brazil is in the process of ratifying its membership in parliament.