This book surveys semiconductor superlattices, in particular their growth and electronic properties in an applied electric field perpendicular to the layers. The main developments in this field, which were achieved in the last five to seven years, are summarized. The electronic properties include transport through minibands at low electric field strengths, the Wannier-Stark localization and Bloch oscillations at intermediate electric field strengths, resonant tunneling of electrons and holes between different subbands, and the formation of electric field domains for large carrier densities at high electric field strengths.