Massive Black Hole Science with eLISA

The evolving Laser Interferometer Space Antenna (eLISA) will revolutionize our understanding of the formation and evolution of massive black holes (MBHs) along cosmic history, by probing massive black hole binaries (MBHBs) in the 10³ - 10⁷ M_o range out to redshift z ≳ 10. High signal-to-noise ratio detections of ∼ 10 - 100 MBHB coalescences per year will allow accurate measurements of the parameters of individual MBHBs (such as their masses, spins and luminosity distance), and a deep understanding of the underlying cosmic MBH parent population. This wealth of unprecedented information can lead to breakthroughs in many areas of physics, including astrophysics, cosmology and fundamental physics. We review the current status of the field, recent progress and future challenges.