The Milky Way in 3D

The space between stars is not empty but filled with a tenuous mix of gas and dust. This matter is partly composed of the remains of previous stars and provides the building blocks for the next generation of stars. This matter absorbs and diffuses light coming from background stars in a process we call interstellar extinction. I will provide a brief review of existing techniques that are used to recover the three dimensional structure of the interstellar medium. I will also introduce ESA's Gaia mission, which will revolutionise many domains of astrophysics through the measurement of accurate distances to 1 billion stars.