  Spintronics is the science and technology of electric control over spin
currents in solid-state-based devices. Recent advances have demonstrated a
coupling between electronic spin currents in non-magnetic metals and magnons in
magnetic insulators. The coupling is due to spin transfer and spin pumping at
interfaces between the normal metals and magnetic insulators. In this Chapter,
we review these developments and the prospects they raise for electric control
of quasi-equilibrium magnon Bose-Einstein condensates and spin superfluidity.
