Gaia is a European Space Agency telescope that started its mission in December, 2013 on board the Russian rocket Soyuz that delivered it to space. Gaia is aiming to map 1 billion stars of our galaxy – approximately 1% of all stars in the The Milky Way! It will do this in the course of a 5 years period and on a Lagrange – 2 point in the Sun-Earth system (meaning 1.5mil. km from Earth, away from the Sun). The L-2 point is convenient, because the telescope will need a steady gravitational force (and almost no fuel) to map accurately while taking snapshots with its 1000MP CCD cameras.
Gaia will transmit data via a high-gain antenna back to Earth.
You can have a look at interesting facts about Gaia here, on this Infographic.
A very interesting 5min. video about how the Gaia mission works.