The European Interferometry Initiative (Eii) is an open association of Institutes and Laboratories willing to collaborate on the exploitation and development of long baseline interferometry in optical/infrared astronomy. The Eii confederates the activities included in the European Commission instruments of the 6th and 7th framework R&D program.

Most of the funding for the activities was obtained through OPTICON - the Optical Infrared Co-ordination Network for astronomy, via WP14 (2013-2016, grant number 312430)  and WP11.2 (2009-2012, grant number 226604).